What is PoW?
It stands for “Proof-of-Work” and it’s an algorithm used in Bitcoin Gold’s code.
Why is needed?
Miners work to calculate hashes to securing the blocks, and are rewarded for that work. The Proof of Work algorithm ensures the rewards are distributed to them in proportion to the share of the work that they do - but does it in a way that does not require trusting anyone to do the distribution.
Why is this important?
Proof of Work is a way of ensuring fairness without giving up power and control to an authority who would need to be trusted - this is the essence of decentralization.
Learn more: Proof of work - Wikipedia