“LARP” stands for Live Action Role-Playing. It’s also frequently assumed that the word “game” is implied (“Live Action Role-Playing Game”), however, LARP can refer to events that do not strictly qualify as being games.
The term is used to refer to a broad variety of different events. While the media most commonly displays medieval fantasy games when talking about LARP, there are murder mystery LARPs, Science Fiction LARPs, etc.
There isn’t a single clear line for what differentiates LARP from certain other forms of improvisational theater, reenactment, etc. Different people disagree on if groups like the SCA (Society of Creative Anachronism) “count” as LARPs or not.” – /R/Larp FAQ