Wall Street and Main Street financial firms embraced bitcoin. Now it's crashing.

This month's trillion-dollar plunge in cryptocurrencies now has a name: the Great Unwind. That's how Mark Cuban labeled the slide that saw the value of bitcoin sink more than 50% in a matter of weeks. 

The billionaire entrepreneur largely attributes the rout to investors borrowing heavily — a way of boosting returns by using "leverage" — to buy up bitcoin competitor ethereum and other digital currencies. Now, the price drop has forced traders to "unwind" their positions to repay that borrowed money. "The minute Eth drops to their Tragic Number, they had to Unwind," tweeted Cuban, referring to ethereum, which has dropped to $2,500, from a high of $4,300, in less than two weeks. "Unstake, Remove Liqudity, Repay."