what is a hash 
a hash is a mathematical function that converts an input of arbitrary length into an encrypted output of a fixed length thus regardless of the original amount of data or file size involved its unique hash will always be the same size moreover secure hashes cannot be reverse engineered to get the input from the hashed output at least with current technology if you use a specific function on the same data its hash will be identical so you can validate that the data is the same i e unaltered if you already know its hash a different function would deliver a different hash hashing is essential to cryptocurrency and blockchain security 