What is the activity of dressing up as a character from a comic book, video game, or television show called?

Cosplay, a portmanteau of "costume play", is an activity and performance art in which participants called cosplayers wear costumes and fashion accessories to represent a specific character. Cosplayers often interact to create a subculture, and a broader use of the term "cosplay" applies to any costumed role-playing in venues apart from the stage. Any entity that lends itself to dramatic interpretation may be taken up as a subject. Favorite sources include anime, cartoons, comic books, manga, television series, and video games. The term is composed of the two aforementioned counterparts - costume and role play.

Cosplay grew out of the practice of fan costuming at science fiction conventions, beginning with Morojo's "futuristicostumes" created for the 1st World Science Fiction Convention held in New York City in 1939. A rapid growth in the number of people cosplaying as a hobby since the 1990s has made the phenomenon a significant aspect of popular culture in Japan, as well as in other parts of East Asia and in the Western world.