What is rem. Deep and core in the sleep tracking app

Hello L-1350!

Those are stages of sleep. The Related Article above your name says this:

“Stages: View the time and percentage you spent Awake or in REM, Core, or Deep sleep.”

BTW, REM= Rapid Eye Movement.

If you want to know more about this, a quick internet search will bring about many results.

I hope this is helpful. Good Luck!