In brief Proof of work is the consensus algorithm that secures the decentralized Bitcoin blockchain network. Bitcoin miners attempt to solve complex math equations with the energy-intensive process, all to generate new blocks and earn BTC rewards. The blockchain technology that powers Bitcoin and many other cryptocurrencies is essentially a database, but it’s far different than any typical, centralized ledger. It’s decentralized and powered by peer-operated nodes distributed all around the world, with no supervising authority to call the shots or set the rules.
So how do you secure a decentralized network and ensure that everyone agrees on the contents of the ledger? That's where Bitcoin's proof of work consensus algorithm comes in.