Because my books deal with a geek-culture niche, I thought I'd take a couple of posts to explain what exactly larping is, how it works, and why it interests me. I'm going to focus largely on my own experience because Lizzie Stark has written an excellent blog and book that go into the variety of games and even into the psychology and theory underpinning all of it in a way I'm not going to try to recreate. Both the book and the blog are called Leaving Mundania.
LARP stands for "live action roleplaying." It's basically an improv acting exercise with two groups of people, players (PCs) and game runners (NPCs), who work together to tell a story in real time. The PCs create characters based on a rule system (so they have various abilities and limitations). They also put in the work of designing costumes, backstories, and personalities. The game runners create a story that the players interact with to solve some sort of problem. They also play all the roles needed to make that story work.
After that, it's hard to say that larping is a single thing. There are zombie larps and space ship larps and vampire larps. In high school and college, I played a fantasy larp that I usually describe as "Dungeons and Dragons, only we ran around in the woods instead of rolling dice." We were psuedo-medieval in our imaginings and costume. In battle, we used boff weapons made from PVC pipe, plumbing foam, and duct tape. We had a simple system--if a sword hits your arm, you lose that arm. Same with legs. Shots to the head, back, or torso killed you. More sophisticated systems rely on calling out points with each strike, but we all liked being able to fight in real time without any pauses for calculations. To get back limbs and life, we had spells. (For a better mental image, there's a YouTube video below that opens with a boff battle.)
Think what you will, but my teenaged friends and I spent almost every weekend in the summer running around outside, collaborating on a 30 person storytelling exercise stories that required some fairly sophisticated organizational and theatrical skills to pull off. Which is a story for another post or two.