Sleep Glossary

Short, clear definitions of the sleep terms that matter most. A reference you can check in seconds.

What is REM sleep?

REM (rapid eye movement) sleep is the sleep stage in which the brain is most active and most dreaming occurs. In an adult, it makes up about 20 to 25% of the night and is concentrated in the second half. It's essential for memory and emotional regulation.

What is the 4-7-8 method?

The 4-7-8 method is a breathing technique to fall asleep faster. You breathe in through the nose for 4 seconds, hold the air for 7 and breathe out through the mouth for 8. Repeat the cycle four times. It slows the heart rate and helps the body calm down before sleep.

What is sleepmaxxing?

Sleepmaxxing is the practice of optimising sleep quality as much as possible through habits, environment and routines. It includes science-based measures — a bedroom temperature between 18 and 19 °C, reduced light, fixed schedules — and others without solid evidence. The term became popular on social media in 2024.

Related guides: Sleep hygiene: 12 habits · How to choose the ideal mattress.