I think definitions about costumes being accurate to what you see on the screen are a bit too restrictive: fans express themselves in a lot of different ways, and things like costume mashups or people reenacting memes or brief, memorable moments from a film, to people who throw something together out of cardboard or scraps is just as valid as the super-accurate builds. That’s a really broad definition, and in the book, miku cosplay I ended up talking about things like the history of Halloween and how it came to become such a big pop-culture holiday.