Salt
A random string added to a password before hashing so two identical passwords don't produce the same hash.
Without salt: 10 users with the password "summer2024" all get the same SHA hash. An attacker with a big "rainbow table" can look up the hash and recover the password. With a unique salt per user, the hash is unique even when passwords match.
Modern hashing algorithms (bcrypt, argon2) generate the salt automatically. You don't have to think about it — but understand why it exists.