Proof of work refers to the hash of a block header (blocks of bitcoin transactions). A block is considered valid only if its hash is lower than the current target. Each block refers to a previous block adding to previous proofs of work, which forms a chain of blocks, known as a block chain. Once a chain is formed, it confirms all previous Bitcoin transactions and secures the network.
A system that ties mining capability to computational power. Blocks must be hashed, which is in itself an easy computational process, but an additional variable is added to the hashing process to make it more difficult. When a block is successfully hashed, the hashing must have taken some time and computational effort. Thus, a hashed block is considered proof-of-work. Proof-of-work is a result that can only be obtained through the use of computational resources. Hashes are cryptographic problems that must be solved in order for a block to be won. Since it is difficult to solve a hash, the solution is proof that a miner put in the effort to get that block. Changing the data in a proof-of-work requires redoing the work. The rewards for this type of mining are that one receives coins and transaction fee rewards in direct correlation to the actual mining work one does. Therefore, the more mining one does, the greater the rewards.
Malone, J.A (2015). Glossary of Bitcoin Terms and Definitions. United States: Lulu Press, Inc
Often seen in its abbreviated form “PoW”, it refers to a mathematical value that can act as the proof of having solved a resource and time consuming computational problem.