A Bitcoin node is a computer that stores a complete copy of the Bitcoin blockchain ledger and runs a program that verifies and relays Bitcoin transactions. Nodes can also act as miners, verifying and validating Bitcoin transactions and including them in newly created blocks.

Nodes play an important role in the Bitcoin network by broadcasting and relaying Bitcoin transactions, thus allowing users to remain anonymous and secure. All Bitcoin nodes are connected to each other, forming a distributed peer-to-peer network. Each node has a copy of the full transaction history and is responsible for verifying new transactions and broadcasting them to the rest of the network. Nodes also help to secure the network by rejecting invalid transactions, as well as relaying valid transactions between peers.

As a result, the Bitcoin network is decentralized, meaning that there is no central authority or server that controls the Bitcoin network.