Sensations in your body.
You asked what is a body scan. The most common use is as part of a meditation practice called mindfulness. It means that you, through a leader-guided experience or a recording, mentally scan your body with awareness, looking and listening for sensations that describe how your body parts are feeling and working. The purpose is for you to be aware of what is going on in your body. Should anything be aroused that may need attention, you may want to watch it and see if it re-occurs. Here is a link for this practice. Have a restful sleep. Chris