Cosplaying is basically wearing a costume based on a fictional character. It is an example of fan culture. While other fans may create fanfiction, fanart and merchandise, cosplayers bring their favorite character to life.
https://www.ccosplay.com/
‘Fan costumes involve four elements: a narrative, a set of clothing, a play or performance before spectators, and a subject or player’ (Lamerichs, 2011). The cosplayer truly becomes the character.