What is a hash?
The word hash refers to the output produced by a hash function. The latter is a mathematical algorithm that converts an input value of any size into an output (hash) of a fixed size.
Any change to the input data will result in a different hash as the output. So, a hash can help verify the validity of information without revealing what this info is. The more difficult it is to find the input value, the more secure the hashing algorithm is.
Cryptographic hash functions are widely used in information security and make an essential part of most blockchain networks. For example, hashing is crucial to Bitcoin mining.