Cosplay - short for "costume play", is basically describing a performing-art behavior of self-rigging out as a character.
There are some wild costumes at in this video. People put in alot of work in their costumes. Duct tape/cardboard technology!
I went to Otafest a few times when it was small. It was interesting but I'm not that big of an anime fan and seeing a 300-pound white guy dressed as sailor moon made my decision not to attend the following year alot easier. To my surprise, it's gotten alot bigger with 4,278 attendees and guests! I might have to check it out next year.