What Is a "Collision Attack" in Cryptography

What is a "Collision attack" in cryptography?

A) Collision attacks try to get the public key.
B) Collision attacks try to break the hash into two parts, with the same bytes in each part to get the private key.
C) Collision attacks try to find two inputs producing the same hash.
D) Collision attacks try to break the hash into three parts to get the plaintext value.