SHA-256 (Secure Hash Algorithm 256-bit) is a cryptographic hash function that is part of the SHA-2 family, designed by the NSA. It produces a 256-bit (32-byte) hash value, typically rendered as a 64-character hexadecimal number.

Key features of SHA-256:

• Produces a fixed-size 256-bit (32-byte) output regardless of input size
• Deterministic: the same input will always produce the same output
• Designed to be one-way: it's computationally infeasible to reverse the hash
• Collision-resistant: it's extremely difficult to find two different inputs that produce the same hash
• Small changes in the input produce completely different hash values (avalanche effect)

Common uses:

• Digital signatures and certificate validation
• Password storage (with proper salting)
• Data integrity verification
• Blockchain technology (including Bitcoin)
• File checksums to verify downloads

SHA-256 is considered cryptographically strong and is widely used in security applications and protocols, including TLS, SSL, PGP, SSH, and many cryptocurrencies.