[quote=@Seirei No Hai]
Co-op as in... Google Docs? First time hearing the term in a roleplay forum X3
[/quote]

Yeah, something like that. It's basically the equivalent of each person doing a really quick back and forth of anywhere between one-liners to one-paragraph posts, but put all together so it doesn't flood the thread. It's good for dialogue-heavy scenes between two characters on their own, since it helps get through them quickly without a lot of tiny posts and spam.