Pick the one you want most

Allows us to better understand your problem

Sleep through the nightFall asleep fasterSleep without pills
Sleep Dictionary: Unraveling the Science of Slumber

Better Sleep Starts Now

Take Your Sleep Quiz
December 18, 2023

Sleep Dictionary

Medically reviewed by: 

Understanding sleep and its terms can be tricky due to scientific language.

In sleep science, technical terms have specific meanings for experts, while some are more casually used.

This sleep glossary aims to demystify essential terminology, offering clear explanations and context to enhance your comprehension of sleep-related concepts. Our objective is to empower you with knowledge from evidence-based resources for better sleep quality.

Ready to take charge of your sleep health? Start with Sleep Reset's sleep quiz, designed to pinpoint your sleep concerns. After your quiz, you can choose to be assigned your own sleep coach and get our dedicated sleep app.


  • Actigraphy: Involves tracking body movement, frequently carried out using wearable devices. It's useful for measuring various activities, including sleep duration.
  • Acute: Describes short-term or sudden sleep issues, contrasting them with persistent or long-term problems termed chronic.
  • Arousal: Denotes the abrupt shift from deeper to lighter sleep stages or waking up. Detecting arousals involves monitoring changes in vital signs or muscle activity in sleep studies.
  • Artificial light: Refers to non-sunlight sources of illumination, often emitted by electronic devices, and particularly the blue light spectrum, impacting our circadian rhythm.
  • Aromatherapy: Involves using scents to influence mental or physical health. In sleep contexts, it aims to induce relaxation at night or enhance alertness during the day.
  • Atonia: Refers to the temporary paralysis of most muscles, typical during REM sleep, except for those controlling essential functions.
  • Awakenings: Represent any waking episode during sleep, discerned in sleep studies by shifts in heart rate, brain, lung, and muscle activities.
  • Bad dreams: Entail negative or bothersome dream content that doesn't cause awakening.
  • BiPAP devices: Are machines supplying pressurized air through the mouth or nose, frequently employed for treating obstructive sleep apnea.
  • Biphasic sleep: Involves two distinct sleep periods within a day, usually a full night's sleep and a daytime nap.
  • Blue light: Comprises a specific wavelength in the visible light spectrum, predominantly emitted by many modern electronic devices, influencing our circadian rhythm more significantly than other light wavelengths.
  • Chronic: Describes enduring or ongoing conditions, often used in sleep contexts to distinguish from acute issues.
  • Circadian alerting system: Brain-mediated signaling promoting wakefulness and attentiveness, governing sleep-wake patterns.
  • Circadian pacemaker: A brain component, the suprachiasmatic nucleus (SCN), regulating the body's circadian rhythm by emitting signals affecting various bodily functions. Light exposure significantly influences its function.
  • Circadian rhythm: The body’s roughly 24-hour internal clock orchestrating various physical and mental functions, including sleep.
  • Chronobiology: Study of natural rhythms influencing living organisms, with sleep science primarily focusing on circadian rhythm.
  • Chronotype: An individual’s distinctive daily sleep-wake activity pattern, reflecting their unique circadian rhythm and personal preferences.
  • Cognitive-behavioral therapy for insomnia (CBT-I): A counseling approach targeting negative thoughts about sleep while promoting better sleep habits, specifically adapted for addressing insomnia.
  • Cognitive impairment: Difficulties in mental functions like thinking, attention, memory, learning, and judgment.
  • Continuous positive airway pressure (CPAP) device: A machine delivering constant pressurized air through the mouth or nose, aiding in maintaining an open airway and reducing sleep apnea. The pressure remains consistent during both inhalation and exhalation.
  • Daytime impairment: Negative effects stemming from sleep issues experienced during wakefulness, encompassing cognitive deficits, physical complications, and emotional or mood disturbances.
  • Deep sleep: The final stage of non-rapid eye movement (NREM) sleep, characterized by decreased heart and breathing rates, slow brain activity, and distinctive delta waves.
  • Delta sleep: The phase of NREM sleep marked by high-amplitude delta waves, known as stage 3, N3, deep sleep, or slow-wave sleep.
  • Diurnal: Activities occurring during the daytime.
  • Dream: Mental images or thoughts during sleep, most vivid in REM sleep. Dreams can be positive, negative, or confusing.
  • Dream recall: The ability to remember dream content after awakening.
  • Electroencephalograph (EEG): A test measuring brain activity using scalp sensors, helping identify sleep cycle stages.
  • Entrainment: The synchronization of an individual’s circadian rhythm with light-dark cycles, influenced by the circadian pacemaker's response to light.
  • Excessive daytime sleepiness (EDS): Drowsiness or difficulty staying alert or awake during daytime hours.


  • Fatigue: A sensation of mental or physical energy depletion, often associated with excessive daytime sleepiness and cognitive decline associated with sleep-related issues.
  • Homeostatic sleep drive: The body's inherent mechanism regulating sleepiness levels. This drive is usually lowest just after waking and escalates the longer a person stays awake.
  • Hormones: Chemical agents transported through the bloodstream, controlling various bodily functions, managed by the endocrine system.
  • Hyperarousal: A heightened state of stress, anxiety, or alertness, linked with insomnia and difficulty falling or staying asleep.
  • Hypersomnolence: Uncontrollable sleepiness during typical waking hours, also termed excessive daytime sleepiness or hypersomnia.
  • Hypersomnia: A sleep disorder typified by excessive sleepiness during expected wakefulness, often interchangeable with hypersomnolence or excessive daytime sleepiness.
  • Hypnagogic: Events occurring around the onset of sleep.
  • Hypnogram: A graphical representation documenting sleep progression during a single sleep session, often derived from a polysomnogram, showing time spent in various sleep stages and instances of awakening.
  • Hypnopompic: Occurrences around the awakening phase from sleep.
  • Hypnotic: Medication inducing drowsiness or sleep.
  • Hypopnea: Abnormally slow or shallow breathing during sleep.
  • Hypoxia: Reduced oxygen levels in bodily tissues, potentially a result of sleep-disordered breathing.
  • Insomnia: A sleep disorder where one struggles to initiate or maintain sleep despite having the opportunity, often leading to daytime dysfunction.
  • Insufficient sleep: An impairment of mental or physical functions due to inadequate sleep duration or frequent sleep disruptions.
  • Jet lag: A condition resulting from desynchronization of the body's circadian rhythm due to rapid travel across multiple time zones.
  • Light sleep: A term commonly associated with stage 1 or N1 sleep, characterized by ease of awakening. It can encompass both stage 1 and stage 2 NREM sleep.
  • Light therapy: A treatment for sleep problems involving brief exposure to intense light, aiming to adjust a person’s circadian rhythm.
  • Long sleep: An extended sleep duration beyond the recommended hours based on age and health.
  • Lucid dream: A dream where the dreamer is aware of being in a dream state.


  • Melatonin: A hormone produced by the body that helps regulate the sleep-wake cycle. It is naturally released in response to darkness and can be found in certain foods. Melatonin supplements are available both as prescription sleep aids and over-the-counter dietary supplements.
  • Metabolism: A collective term encompassing various bodily processes involved in the creation and utilization of energy.
  • Microsleep: Brief episodes of sleep that last only a few seconds and are often linked to excessive daytime sleepiness.
  • Monophasic sleep: A sleep pattern where a person's entire daily sleep occurs during a single, continuous sleep period.
  • N1 sleep: The initial stage of non-rapid eye movement (NREM) sleep, also known as stage 1.
  • N2 sleep: The second stage of NREM sleep, known as stage 2.
  • N3 sleep: The final stage of NREM sleep, also known as stage 3, deep sleep, delta sleep, or slow-wave sleep.
  • Nap: A short period of sleep, usually taken during the day and distinct from a person's main sleep period. Sometimes referred to as a siesta.
  • Natural light: Illumination produced by the sun.
  • Neurotransmitter: A chemical that aids communication between brain cells, affecting various physical and mental functions, including sleep regulation.
  • Nightmare: A distressing dream causing awakening during sleep, typically remembered upon waking.
  • Nocturia: Frequent nighttime urination, often involving waking up one or more times to urinate.
  • Nocturnal: Activities occurring during the night.
  • Non-rapid eye movement sleep (NREM): One of the two main sleep types consisting of stages N1, N2, and N3. NREM sleep involves reduced brain and body activity compared to wakefulness.
  • Partial sleep deprivation: A condition where sleep duration is less than the recommended amount but not completely absent.
  • Pharmacotherapy: Treatment involving the use of medications, including prescription drugs.
  • Polysomnography: A specialized sleep study that monitors various parameters like brain waves, muscle activity, and eye movement, often used for diagnosing sleep disorders.
  • Positive airway pressure (PAP) device: A machine delivering pressurized air through the nose or mouth to maintain an open airway during sleep, primarily used for obstructive sleep apnea.
  • Rapid eye movement (REM) sleep: A sleep stage with heightened brain activity, vivid dreaming, and temporary muscle paralysis, primarily occurring in the latter part of sleep.
  • REM rebound: Increased time spent in REM sleep following a period of reduced total sleep or REM sleep.


  • Screen time: The duration spent using electronic devices such as mobile phones, tablets, laptops, computers, and televisions.
  • Sedative: A substance or medication that induces drowsiness.
  • Shift work: Employment that requires non-standard work hours, often involving evening or overnight schedules, distinct from the typical 9 a.m. to 5 p.m. workday.
  • Short sleep: Sleep duration below the recommended amount based on age and health.
  • Sleep aid: Any substance or medication used to improve sleep, including prescription drugs, over-the-counter medications, dietary supplements, and alternative approaches like aromatherapy.
  • Sleep apnea: A sleep disorder characterized by disrupted or irregular breathing, including obstructive sleep apnea and central sleep apnea.
  • Sleep architecture: The cyclical arrangement of sleep stages, such as NREM and REM, often depicted through a hypnogram.
  • Sleep bruxism: Grinding or clenching of teeth during sleep.
  • Sleep continuity: Sleeping without interruptions or awakenings for a period.
  • Sleep cycle: A progression through various sleep stages during a single sleep episode, typically occurring 4-6 times a night.
  • Sleep debt: Accumulated lack of sleep over an extended period.
  • Sleep deficiency: Inadequate rest, stemming from either reduced sleep duration or fragmented sleep patterns.
  • Sleep deprivation: Insufficient sleep duration relative to recommendations for age and health.
  • Sleep disturbance: Any factor causing sleep interruption or arousal.
  • Sleep duration: Total time spent sleeping during a sleep period.
  • Sleep efficiency: The percentage of time spent asleep compared to total time in bed.
  • Sleep environment: Surroundings impacting sleep quality, including factors like mattress, lighting, noise, and temperature.
  • Sleep fragmentation: Disruption in sleep marked by repeated arousals or awakenings.
  • Sleep hygiene: Personal practices and routines influencing sleep quality and sleep-related issues.
  • Sleep inertia: A period of grogginess upon awakening.
  • Sleep latency: The duration between bedtime and falling asleep.
  • Sleep maintenance: Ability to stay asleep for the intended duration.
  • Sleep onset: The commencement of sleep.
  • Sleep pattern: A person's sleep schedule and habits.
  • Sleep phase: The timing and nature of a person's typical sleep.
  • Sleep quality: Individual satisfaction with the sleep experience, considering various sleep aspects.
  • Sleep regression: A deterioration in sleep quality in infants or toddlers following an improvement.
  • Sleep stages: Different segments of the sleep cycle, encompassing NREM and REM sleep.
  • Sleeping position: Posture during sleep, like side, back, or stomach sleeping.
  • Slow-wave sleep: Stage 3 of NREM sleep characterized by specific brain wave patterns.
  • Somnolence: The state of feeling drowsy or sleepy.
  • Snoring: Audible tissue vibration in the throat, often associated with chronic or primary snoring.
  • Soporific: Inducing drowsiness.
  • Suprachiasmatic nucleus (SCN): Brain region controlling the body's circadian rhythm.
  • Time in bed: Total time spent in bed irrespective of actual sleep.
  • Total sleep deprivation: A period without any sleep.
  • Total sleep time (TST): Duration of actual sleep during a planned sleep period, including both REM and NREM sleep.
  • Vivid dream: Highly immersive or clear dream episode.
  • White noise: Sound blending all audible frequencies at equal amplitude.
  • Zeitgeber: Factors influencing the synchronization of circadian rhythm to the day-night cycle, with light being a dominant zeitgeber.

Start Sleeping Better With Sleep Reset Today!

If you're looking for a drug-free way to get better sleep, the Sleep Reset program can help. We use CBT-I principles to help you fall asleep and stay asleep all night. Our free sleep quiz can help you identify the underlying causes of your sleep problems, so you can find the best solution for you.

Our program does not rely on harmful pills, melatonin or supplements – which means no grogginess, dependency, or long-term health risks. Instead of relying on quick fixes, we use proven techniques to address the root causes of your sleep issues and give you the long-term tools to manage your sleep. Our dedicated sleep coach will help you via daily text to provide accountability, support, and guidance.

The Sleep Reset program is available on iOS and Android.

Take the Sleep quiz now.