The term node can have several meanings depending on the context. It may refer to:

Node (DOM)
In the context of the DOM, a node is a single point in the node tree. Various things that are nodes are the document itself, elements, text, and comments.
Node (networking)
In networking, a node is a connection point in the network. In physical networks, a node is usually a device, like a computer or a router.

Another use of the word is when talking about Node.js