A fixed-length alphanumeric string produced by running data through a cryptographic hash function. In blockchain, each block contains the hash of the previous block, creating a tamper-proof chain. Hashes are deterministic, meaning the same input always produces the same output.
Example
“Every Bitcoin block header contains the hash of the preceding block, such as '00000000000000000002c5...', ensuring that altering any past transaction would break the chain.”