Whilst is defined as while and refers to things going on at the same time as something else.
If you fall asleep as you are watching a movie, this is an example of a situation where you fall asleep whilst watching a movie.
Chiefly Brit. while
Origin of whilstMiddle English whilest, extended ; from whiles, whiles
Origin of whilstMiddle English whilest, alteration of whiles, whiles; see whiles.
- (chiefly UK) While, at the same time.