A hash is a one-way fingerprint of data: the same input always produces the same fixed-size output, but you can't run it backwards to recover the input. Type below to hash live with three algorithms, then use the avalanche lab to see how changing a single character rewrites roughly half the output.
Collisions are trivial to produce. Fine for checksums, never for security.
A real collision was demonstrated in 2017 (Google's “SHAttered”). Retired from security use.
No known collisions. This is the hash securing Bitcoin and Ethereum.