Scrypt is a PoW-algorithm constituting an alternative to SHA-256. Scrypt is used in Bitcoin mining. When you mine through Scrypt, you rely more on memory than central processing power. The rationale behind this is to even out the playing field between “regular miners” and miners using ASICs (as the users of ASICs otherwise have a great advantage over non-ASICs miners). By evening out the playing field, the hope is that it will increase network participation and energy efficiency.