What Is Hash?
A hash is a fixed-length output produced by a cryptographic hash function from any input data. Bitcoin uses SHA-256, producing a 64-character hexadecimal string regardless of whether the input is a single character or an entire book. Hashes are deterministic (same input always produces same output), one-way (you can't reverse a hash to find the input), and collision-resistant (virtually impossible to find two different inputs with the same hash).
How Hash Works
Hashes are fundamental to blockchain operation: each block's header contains the hash of the previous block, creating the "chain" in blockchain. Any change to a past block would change its hash, invalidating all subsequent blocks. Transaction IDs (TXIDs) are hashes of transaction data. Merkle trees use hashes to efficiently summarize all transactions in a block.
Why It Matters for Traders
For traders, hashes are mostly behind-the-scenes infrastructure, but understanding them explains why blockchains are secure and immutable. The hash rate (total computational power mining a network) directly affects security and, through mining economics, can influence sell pressure. Transaction hashes (TXIDs) are used to track specific transactions across block explorers.
