Role-playing is immersion to an outside consciousness ("a character") and interacting with its surroundings. - Mike Pohjola
A larp is a meeting between people who, through their roles, relate to each other in a fictional world. - Eirik Fatland & Lars Wingård
Larp is a medium, an interactive and collaborative form of storytelling in which participants take on personas other than themselves and physically interact as those personas in a shared, imagined diegesis, under the guidance of a set of rules or mechanics governing those interactions. - Adina Schreiber
Larp is originally an acronym for Live Action Role Playing, but today it’s used as name in itself. It refers to a type of interactive game or storytelling in which the players assume a role and act as a character within the set fiction. It can be described as theater without an audience or script.
For more info about what larp is from various sources, including videos, check here.
If you want to know how to start larping, click here.
If you want to know how to organize a larp, click here.