Peer
Another node that yours connects to in order to exchange blocks and transactions.
A peer is any other node that your node maintains a connection with to swap blocks, transactions, and the addresses of further nodes. A healthy node keeps connections to several peers at once, some dialled out and some dialled in, so that no single broken link isolates it. Peers are discovered without any central directory: a fresh node bootstraps from a few known starting points, then learns about more peers from the ones it reaches. This gossip-based discovery is what makes the network leaderless and resilient. Peer count is also the most useful health signal: zero peers usually points to a connectivity or firewall problem on your machine.