'Daemon' is the general term for a piece of software running in the background. In Haven, the Daemon is started through the 'havend' program. If you run the Daemon locally, you are running a local node. If the Daemon is running on another device it's a @remote-node. A @wallet, like the CLI or the GUI, needs to connect to a Daemon (local or remote) to relay @transactions to the network.
It's possible to send commands to the Daemon directly or through the RPC interface. See the Daemon RPC guide, which contains a detailed explanation (with examples) of the available RPC calls. For more detailed and technical information about the Daemon, see the Havendocs reference at the bottom of this page.