Larp is short for "live-action roleplay". It consists of people playing out fictional roles within some kind of organized framework. It can be playing the roles of all fifty members of a space ship crew within the framework of a three-day event including a complete spaceship scenography and game organizers playing the parts of alien races. Or it can be playing the roles of ten hungry soldiers within the framework of an hour-long session taking place in a regular school classroom, ending with a debrief where the participants discuss the dynamics of group pressure.
Larp is a relatively new medium, and there are many sub-genres or forms. At the Larpwriter Summer School, we look mostly at the forms of larp that are easily usable by people working with education - both formal education, like school teachers, and non-formal education, like volunteers for charity organizations. This includes larps that are relatively easy to set up and run, with inexpensive techniques for creating a good playing space. However, we like to think that the basics of larp design are similar across many forms of larp and so we look at many different kinds of larp at the Summer School.
We believe larp can be a powerful medium both for recreation and for education. It is totally interactive, and allows for everyone to participate at the same time. Playing out a fictional situation can evoke reflection about similar real-world situations. Actively being part of and shaping a story can be much more enjoyable than passively observing a story, and larp can be a way to encourage involvement in a subject matter.
There is a lot of documentation about different kinds of larp on the web. As a starting point, you may want to look at: