A sleepover is a social occasion whereby a friend stays overnight at another friend's house. A pajama party or slumber party is essentially the same thing, but may involve multiple people. A lock-in again involves multiple people, but it differs in that it is held in a setting other than a private home, such as a school or church. In all of the aforementioned, it is implicit that the participants are young people, perhaps children or teenagers. The goal of these events is simply to have fun with others. Unlike a traditional play date, however, sleepovers up the ante by having the participants sleep together. This may introduce some social dynamics not normally present in a typical get-together.
