Scrypt is a key derivation function designed for hashing passwords with a controllable difficulty parameter to reduce the efficacy of brute force attacks. It was created by Colin Percival in 2009. Scrypt is designed to use a large amount of memory, in addition to computational resources to reduce the efficacy of specialised hardware attacks such as the use of FPGAs or ASICs.
Details about the specification can be found in RFC 7914 https://datatracker.ietf.org/doc/rfc7914/.