DEFINITION of Full Node
BREAKING DOWN Full Node
Each computer that joins a bitcoin network is called a node of the network.
Most of such computers join the network for performing basic activities - like validating the authenticity of transactions and earning from mining - and are called lightweight nodes. They only download block headers, which is sufficient for performing their limited activity.
A few computers on the blockchain are the special ones which download every single block and the transactions presented to it, and verify them against the core consensus rules of the blockchain network. Such computers are called full nodes. Core consensus rules cannot be changed, unless done through a hard fork which results in a new blockchain with a new identity.
A lightweight node may mistakenly assume the validity of a transaction or a block, but the full nodes will reject it absolutely.
Essentially, full nodes form the backbone of the virtual currency network, as these are the major contributors that maintain the sanctity and trustless nature of the globally distributed blockchain network.