Rest can be any restful period, not necessarily sleep. Rest includes naps, meditation, breathing exercises - whenever the ring detects that you're resting. Sometimes rest can be just laying on the sofa and watching TV or reading a book. Oura uses several measurements including your movement and temperature to detect restful periods.
Rest is currently not taken into account in calculating Readiness.
Rest is shown in the app’s main view when scrolling down the page.
Rest reports include your lowest resting heart rate, as well as average HRV if the measurement quality has been good enough.