Cryptocurrencies such as Bitcoin are mostly decentralized. In other words, they operate without an intermediary or central authority, and as such, do not depend on a single entity to verify transactions or add data to the blockchain. They are best described as a mesh of active participants distributed across the network in the form of varying constituents (full, light, or minor nodes) who, depending on their role, validate and verify incoming transactions. This is where Proof-of-Work comes in.
Proof-of-Work (or PoW for short) is a consensus mechanism used to choose the network participants who verify data and validate transactions. In simpler terms, it is a consensus mechanism that enables anonymous parties to trust each other and transact in decentralised networks.