The Merriam-Webster dictionary defines cosplay as "the activity or practice of dressing up as a character from a work of fiction (such as a comic book, video game, or television show)" The origins of cosplay are discussed here: http://www.strangelandcostumes.com/history.html
LARP is an acronym for Live Action Roleplay. According to the online Collins English dictionary, LARPing is "a type of role playing game in which each participant assumes a particular character and acts out various scenerios at events which liast for a predetermined time."
The online Collins English dictionary defines steampunk as: "1. a genre of science fiction that combines futuristic elements with a quasi-Victorian setting."