Can anyone tell me in precise and simple terms what constitutes a node? I read Satoshi's white paper but it is still unclear to me who counts as a node.
For example, which of these are nodes and which are not: a mining pool, an individual in a mining pool, a solo miner, and an individual running the client but not mining.
A node is a participant in the transaction relaying network, and can provide a partial block header to answer a getwork RPC request.
The bitcoin client is a node.
Mining pool software is not a node, but it requires a connection to a node (usually running on the same box). Mining clients are not nodes, but they require a connection to either a node or to a pool (which is in turn connected to a node).