Published by Actually Sleeping · Reviewed by Dr. Samantha Abrahamson, PharmD · Review policy · Updated 2026-11-10

Baby sleep glossary: 40 terms parents hear, in plain English

Most baby sleep jargon falls into three groups: timing (wake window, sleep pressure, circadian rhythm), how a baby falls asleep (sleep association, self-settling, drowsy but awake) and safety (SIDS, SUID, room sharing, safe sleep). Below, 40 terms are defined in one to three plain sentences, methods are described without endorsement, and safety facts link to AAP, CDC and NIH sources.

40 terms, alphabetical, each in one to three sentences. Methods are described, not recommended. Safety and research statements are taken from the AAP, CDC, NIH and peer-reviewed sources listed at the bottom. Each term has its own link, for example /guides/baby-sleep-glossary/#wake-window.

Knowing the words is the first step. Knowing which of them explains your baby’s nights is harder, and that is what Actually Sleeping works out with each family: a sleep plan written for that baby, with bootcamp-style coaching before the first night and daily 1:1 check-ins.

Jump to a term

Active sleep · Bed sharing · Bedtime fading · Camping out · Catnap · Chair method · Circadian rhythm · Cluster feeding · Contact nap · Corrected age · Dream feed · Drowsy but awake · Early rising · Extinction · False start · Graduated extinction · Melatonin · Nap transition · Night weaning · Overtired · Quiet time · REM sleep · Room sharing · Safe sleep · Self-settling · SIDS · Sleep association · Sleep cycle · Sleep debt · Sleep pressure · Sleep regression · Sleep sack · Split night · SUID · Swaddle · TOG · Undertired · Wake window · White noise · Witching hour

The terms

Active sleep: The newborn version of REM sleep: eyes may flicker, breathing is irregular and the baby twitches or grimaces. Newborns fall asleep through this stage rather than through quiet sleep, which is one reason they rouse so easily.
Bed sharing: A baby sleeping on the same bed, sofa or other surface as an adult or child. The AAP recommends avoiding bed sharing under any circumstances, including with twins and other multiples.
Bedtime fading: A method that temporarily moves bedtime later, to when a child reliably falls asleep quickly, then moves it earlier in small steps. In a 2016 randomized trial it shortened the time infants took to fall asleep. More in bedtime fading.
Camping out: A parent-present method: the parent stays in the room while the child falls asleep and moves gradually farther away, and eventually out, over a series of nights. The term is often used interchangeably with the chair method.
Catnap: A short nap, often one sleep cycle or less. Parents also use it for the brief late-afternoon nap many younger babies take before bedtime.
Chair method: A method in which a parent sits on a chair beside the crib at bedtime and moves the chair a little farther away every few nights until it is out of the room. See the chair method.
Circadian rhythm: The body’s roughly 24-hour clock, which times sleepiness, alertness and hormones. In babies it develops at around 2 to 3 months, which is why newborn sleep is scattered across day and night.
Cluster feeding: A widely used term for a stretch of very frequent feeds close together, common in newborns and young infants, often in the evening hours.
Contact nap: A nap a baby takes while being held or worn by an adult. If you might fall asleep, the AAP says to put the baby in their own sleep space first; it notes the risk of sleep-related death is up to 67 times higher when infants sleep with someone on a couch, soft armchair or cushion. See how to stop contact napping.
Corrected age: For a baby born early, age from birth minus the number of weeks born preterm (40 minus gestational age at birth). The AAP suggests using it during the first 2 years to judge when to expect developmental milestones.
Dream feed: A feed given to a sleeping baby, usually late in the evening before the parent goes to bed, without fully waking the baby. Some families use it to try to shift the baby’s longest stretch later. See does a dream feed work.
Drowsy but awake: Putting a baby into the crib relaxed and sleepy but still awake, so the final step of falling asleep happens in the crib. It is a common suggestion for helping a baby learn to fall asleep independently.
Early rising: Waking for the day earlier than the family wants and not going back to sleep. It is a parent-defined problem, not a medical diagnosis. See early morning waking.
Extinction: A method in which a parent puts the child to bed at a set time and does not return until morning, except for safety or illness. Researchers call it unmodified extinction; a 2006 AASM review found strong research support for it. See extinction explained.
False start: A waking soon after bedtime, often 30–45 minutes in, as if the first sleep cycle had been a nap. See false starts at bedtime.
Graduated extinction: A method in which a parent leaves and returns for brief checks at intervals that lengthen over time. In a 2016 randomized trial it reduced time to fall asleep and night awakenings, with no differences in emotional or behavioral problems or attachment at 12-month follow-up. See graduated extinction explained.
Melatonin: A hormone the body releases in darkness that signals nighttime; in babies a day-night melatonin rhythm appears by about 3 months. In the U.S. it is also sold as a supplement that the FDA does not regulate like medicines, and the AAP says to use it only after talking with your pediatrician.
Nap transition: The weeks during which a child drops from one number of naps to fewer, for example from 3 naps to 2 or 2 to 1. Days are often mixed during the switch. See nap transitions.
Night weaning: Gradually or fully stopping feeds during the night. Whether and when a baby no longer needs night feeds is a decision for your pediatrician. See night weaning.
Overtired: A parent term for a baby who has been awake too long for their age and becomes harder, not easier, to settle. It is a practical description rather than a medical diagnosis. See overtired baby.
Quiet time: A rest period in a child’s room, usually after a toddler or preschooler stops napping, where the child plays quietly instead of sleeping.
REM sleep: Rapid eye movement sleep, the lighter, dream-associated stage. In infants a full cycle of non-REM and REM sleep lasts about 50 minutes, compared with about 90 minutes in adults.
Room sharing: The baby sleeps on their own safe surface in the parents’ bedroom. The AAP recommends it for at least the first 6 months and says it can decrease the risk of SIDS by as much as 50%.
Safe sleep: The set of practices that reduce sleep-related infant death: back to sleep for every sleep, a firm flat surface, nothing soft in the sleep space, and room sharing without bed sharing. The AAP says any surface inclined more than 10 degrees is not safe for sleep. See safe sleep and sleep training.
Self-settling: Falling asleep, or back to sleep after a waking, without an adult’s help. Also called self-soothing or independent sleep.
SIDS: Sudden infant death syndrome: the sudden death of a baby younger than 1 year that has no known cause even after a full investigation. It is one type of SUID.
Sleep association: Something a child links with falling asleep, such as feeding, rocking, a pacifier or a parent’s presence. It matters most when the child needs it again to return to sleep after normal night wakings. See feed-to-sleep association.
Sleep cycle: One round of non-REM and REM sleep. Infant cycles last about 50 minutes, and a brief partial waking between cycles is normal. See how infant sleep cycles develop.
Sleep debt: The running shortfall between the sleep a person needs and the sleep they get. Parents use it loosely for a child who has had several short nights or short naps in a row.
Sleep pressure: The drive to sleep that builds the longer someone is awake and eases during sleep. It is the idea behind wake windows: enough pressure helps a baby fall asleep, too little makes settling slow.
Sleep regression: A popular term for a stretch, often around 4, 8–10, 12 or 18 months, when a child who was sleeping well starts waking more or fighting naps. It is not a medical diagnosis. See the 4-month regression.
Sleep sack: A wearable blanket. The AAP prefers infant sleep clothing over loose blankets, says sacks that do not swaddle and let the baby move freely can be used as long as you want, and says not to use weighted blankets, sleepers, swaddles or other weighted objects on or near your baby.
Split night: A long stretch of wakefulness in the middle of the night, often 1–3 hours, with the child calm or playful rather than upset. See split nights.
SUID: Sudden unexpected infant death: a sudden, unexpected death of a baby younger than 1 year. It is the umbrella category that includes SIDS, accidental suffocation in a sleeping environment, and deaths from unknown causes.
Swaddle: Wrapping a baby snugly in a thin blanket or swaddle product with the arms in. The AAP says to stop as soon as a baby shows signs of trying to roll, to leave room for the hips to move, to avoid overheating, and says there is no evidence to recommend swaddling as a way to reduce SIDS risk. See swaddle transition.
TOG: Short for thermal overall grade, a rating of how much warmth a fabric holds in. The higher the tog value, the more insulation; you will see it on some sleep sacks.
Undertired: A parent term for a child put down before enough sleep pressure has built, who then plays, chats or takes a long time to fall asleep. Like overtired, it is a practical description, not a diagnosis.
Wake window: The stretch of time a baby is awake between one sleep and the next. Age-based wake window ranges are rules of thumb from practice, not research findings. See the wake window calculator.
White noise: A steady, even sound used to mask household noise during sleep. In a 2014 study, all 14 infant sleep machines tested could exceed 50 decibels at 30 cm, so volume and distance from the crib matter.
Witching hour: A parent term for a regular period of evening fussiness in young babies. The AAP’s parent site notes fussy periods often fall between 6 p.m. and midnight.

Where the numbers come from

Figures in these definitions (cycle length, room-sharing guidance, the 10-degree incline limit, sound levels) are on the baby sleep statistics page or in the references below, each checked on the source page.

From terms to a plan

The methods above are defined for reference only. Actually Sleeping does not use cry it out (extinction) and does not ask families to wait it out. Instead, a plan is written for your baby’s age, feeds, temperament and current sleep associations, naps are coached until solid, and the plan never asks you to drop night feeds; feeding decisions stay with your pediatrician. Parents describe the results in the client video reviews.

If you recognize your baby in more of these terms than you would like, book the free consultation.

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Frequently asked

What is the difference between SIDS and SUID?

SUID, sudden unexpected infant death, is the umbrella term for any sudden, unexpected death of a baby under 1. SIDS is one type of SUID: a death with no known cause even after a full investigation. Accidental suffocation in a sleeping environment is another type.

Is a sleep regression a medical condition?

No. It is a popular term for a period when a child who was sleeping well starts waking more or resisting naps, often around developmental changes. If sleep changes come with fever, pain or other symptoms, call your pediatrician.

What is the difference between extinction and graduated extinction?

In extinction, the parent does not return after bedtime except for safety or illness. In graduated extinction, the parent returns for brief checks at intervals that lengthen over time. Both are behavioral methods studied in research; neither is required to improve a child’s sleep, and Actually Sleeping uses neither.

Are wake windows based on research?

No. Age-based wake window ranges are practice conventions. The research recommendation is total sleep per 24 hours: the AASM gives 12–16 hours at 4–12 months and 11–14 hours at 1–2 years, and none under 4 months.