A one-way transformation of data to a compact representation.
A hash is a series of random numbers and letters that represents some data. Hashes have certain properties that make them great for use in blockchains:
They are unique. Even the smallest change to the original data makes a vastly different hash. This makes tracking changes easy. Because one hash can only represent one piece of data, it is collision resistant; it's highly unlikely to be represented by the same hash (about 1 in 2^128).
No matter how large the original data is, the hash will always be the same length.
Hashes allow one-way encryption, which means it's impossible to reconstruct the original data from the hash representing it.
An image and its hash
Hashes are crucial in things like securing passwords and maintaining the integrity of blockchain transactions. For Polybase, hashes are the representation of transactions that have been validated on our network.