A live action role playing game  is also known as LARP and it is when a game played with participants and they physically portray whatever character they are assigned.
I've never heard of the term LARP!  What games are they?
The participants pursue their goals in the real world while staying in character and interacting with other characters.
Oh so it's not a video game?  Are they in a certain place or just anywhere?
The outcome of the participants actions are governed by rules which can be determined among a consensus of players,.
how many players are there at a time?
No. Not a video game. THere are event arrangers and their title is gamemasters who decide the setting and rules to facilitate the play.