First of all, what’s a hash? A hash is the output of a one-way, reproducible function for creating a small fingerprint from a chunk of data. For example, when the popular hash function MD5 is given the word “cat”, it produces the following output every time:
If “cat” is changed to “cats” the resulting hash is completely different:
No matter how much data the hash function is given, the fingerprint stays the same size. No matter how small the change to the data, the fingerprint will be totally different.