Collision resistance is a fundamental property of cryptographic hash functions like SHA-256. It means that it's computationally infeasible to find two different input data (messages) that produce the same hash value (digest). In other words, a collision occurs when two different inputs result in the same output hash value.

Collision resistance is a critical property for various applications, including:

1. Data integrity: Ensures that two different data sets cannot produce the same hash value, maintaining data integrity.

2. Digital signatures: Prevents an attacker from finding an alternative input data that produces the same hash value, ensuring the authenticity of the signed data.

3. Data compression and deduplication: Ensures that two different data sets cannot be compressed or deduplicated to the same hash value, maintaining data uniqueness.

Collision resistance is a stronger property than pre-image and second pre-image resistance, as it requires finding two different input data that produce the same hash value, rather than just recreating the original input data or finding a different input data with the same hash value.

SHA-256 is considered collision-resistant, meaning it's computationally infeasible to find two different input data that produce the same hash value. This property makes SHA-256 a reliable and secure hash function for various applications.