The terminology used through Plane9.

Project

Contains references to scenes.

Scene

Has a number of nodes and the connection between them. These scenes are then referenced from a Project. Only scenes can be edited in the editor.

Node

A single work entity. The node is where the action happens.
Example of nodes are pingpong, Convert XYZ value to a vector and clear screen.
A node uses multiple ports to get to know how you want it to work.

Port

The data that goes into and out of a node goes though a port.
It's the nodes access to the outside world.
This can be a simple integer value or something more complex like a vector or even a effect to be applied to a mesh

Connection

Allows data to flow between two ports.