Hashing is the process of converting plaintext passwords into a fixed-length, irreversible string using a mathematical algorithm (hash function). This makes each password unique based on its content, and even a small change in the password will produce a different hash. The primary purpose is to ensure that the actual passwords are not stored directly and cannot be easily recovered from the hash, even if the hash is compromised.
Reference:
CompTIA Security+ SY0-701 Official Study Guide, Domain 1.3, "Hashing ensures that plaintext passwords are not stored directly. Hash functions use mathematical algorithms to produce unique, fixed-length output for each unique input." Exam Objectives 1.3: "Explain the importance of cryptographic concepts."