Hedge funds shorted more than 100% of all shares of gamestop, to do this that means they had to sell more shares than actually existed.

Whole post is worth reading. It’s all old hat to me but is mostly accurate.

Also, it’s worth pointing out that if hedge funds shorted more than 100% of all shares of Gamestop at the same time, then someone was naked shorting (shorting shares they didn’t actually borrow), which is illegal. Not that it matters — we don’t enforce it, so hedgies do it all the time.