Definition: Dressing up in costumes. Often characters from anime or video games.
A portmanteau of "costume" and "play".
It has become a common sight at fan conventions.
A cosplayer (コスプレイヤー) is someone who performs the act of cosplaying. This term can be shortened to Rayer/Layer, which Nobuo from AkibaRanger often does.
Almost all the characters in Hikounin Sentai AkibaRanger do cosplay as some point during the show.