Oh man, why didn't I find this before Halloween? Cosplay is short for costume play. Basically a movement that started in Japan where people dress up as their favorite comic book/anime/fantasty movie character. Started in the mid 1980s, it's turned into an underground subculture movement where people are expected to meticulously imitate one's character. Recently, with the rise of science fiction/fantasy movies, non-Japanese characters from movies like the Matrix or Lord of the Rings are included under this term, cosplay. You can read all about this phenomenon on Wikipedia or you can just look at all these crazy costumes. Wild! Hun, don't get any ideas...I'm way too old for this!
Source and more: It's Knuttz