A sleepover is a night you spend sleeping at a friend's house. Some sleepovers are large gatherings of many pajama-wearing friends, while overs consist of just two people.
If you're invited to a sleepover, you'll want to pack a sleeping bag, your toothbrush, and pajamas. Kids and teenagers are the most likely to attend sleepovers, which often mark the first time a child has slept away from her own bed. When a sleepover involves a group of friends, you can also call it a slumber party or pajama party. Sleepover has been used since the 1930s.