yescrypt is a password-based key derivation function (KDF) and password hashing scheme. It builds upon Colin Percival's scrypt and includes classic scrypt, a minor extension of scrypt known as YESCRYPT_WORM (named that for "write once, read [potentially] many [times]", which is how scrypt works), and the full native yescrypt also known as YESCRYPT_RW (for "read-write").
Like it or not, password authentication remains relevant (including as one of several authentication factors), password hash database leaks happen, the leaks are not always detected and fully dealt with right away, and even once they are many users' same or similar passwords reused elsewhere remain exposed. To mitigate these risks (as well as those present in other scenarios where password-based key derivation or password hashing is relevant), computationally expensive (bcrypt, PBKDF2, etc.) and more recently also memory-hard (scrypt, Argon2, etc.) password hashing schemes have been introduced.