Definition of Proof-of-Work
POF is a protocol which is commonly used in much of cryptographic applications. This is helpful in the generation of a block in a distributed blockchain based network. Every miner has to complete their proof of work in order to accept a block by network participants. Hash cash is one of an application of this method.
Breif Explanation of Proof-of-Work
It Is very important in a current era of cryptocurrency world like bitcoin uses proof of work software name ase than once so the Hashcash being a proof of work regulate the all these transactions in a block chain to assure that not a single bitcoin has been used more than one time with the intention of falsification.