What does the term "collision" refer to in hashing?

In the context of hashing, the term "collision" specifically refers to the scenario where two different inputs produce the same hash output. This is a significant concern in hash function design, as one of the primary goals of a good hash function is to ensure that the likelihood of such collisions is extremely low. When a collision occurs, it can undermine the integrity of systems that rely on hash functions for tasks such as data integrity verification, password storage, and digital signatures.

Collisions can lead to security vulnerabilities, such as the ability for an attacker to substitute a malicious input for a legitimate one without detection, as both would yield the same hash value. Therefore, the concept of collisions is critical for understanding the effectiveness and reliability of hash functions in cryptographic applications.