Proof of Work (PoW) is a consensus algorithm used by some blockchains, most notably Bitcoin, to secure the network and validate transactions. In a PoW system, miners compete to solve complex cryptographic puzzles, and the first one to solve the puzzle gets the right to add a new block to the blockchain.
The process requires substantial computational power and energy. The PoW mechanism provides security to the blockchain, as altering any past information would require redoing the work of subsequent blocks, which is practically infeasible. However, PoW has been criticized for its high energy consumption and environmental impact.