Full Node
In short: A full node is a computer running blockchain software that downloads the entire blockchain history and checks every block and transaction against the…
A full node is a computer running blockchain software that downloads the entire blockchain history and checks every block and transaction against the network's rules. By observing the chain and rejecting anything invalid, full nodes enforce the rules the network has established.
Why it matters
A full node does not need to trust anyone else's data. If a miner or validator produces a block that breaks a rule, for example by spending coins that do not exist, full nodes simply reject it. The more independent full nodes a network has, the harder it is to change its rules without broad agreement. Running one also lets you verify your own payments instead of relying on someone else's server, as light wallets do. Some full nodes delete old block data after checking it to save disk space, but they have still verified everything themselves. Running a full node is not the same as mining: it validates and relays blocks but does not produce them. Exchanges, EX5 included, use nodes to detect incoming deposits and count confirmations before crediting an account.
Example
A user installs Bitcoin Core on a home computer. The software downloads every block since the genesis block and checks each transaction's signatures and that no coin is spent twice. Once it has caught up, the user's wallet can confirm incoming payments on its own, without asking anyone else whether they are valid.