Proof of Work (PoW)
Plain English
The original consensus method used by Bitcoin. Miners compete to solve complex math puzzles using lots of computer power. The first to solve it gets to add the next block and earn rewards. Very secure but uses massive amounts of electricity.
Technical
Consensus mechanism where miners compete to solve cryptographic puzzles (hash functions) requiring significant computational work. The first to find a valid solution broadcasts the block and earns mining rewards. Security comes from the computational cost of attacking the network (would require 51% of total hash power). Energy-intensive but battle-tested over 15 years.