I've never participated in cosplay -- doesn't appeal to me at all, but that's just me.
The Comic Con conventions, etc., were how it was described to me by a work friend -- she and her DH are really into it. A few people or couples, whatever and however many, get together and act out scenes from movies, books, etc., or written by individuals in the play. Costumes, faked accents, props, however fancy you wish to do it, are generally a part of it. Many folks play with the same folks and they really get into it. My work friend and her DH get somewhat off the beaten track, IYKWIM, but I've never wanted to hear about kink, etc., so I've got no details there.