Geometry nodes system for modifying the geometry of an object with node-based operations. It can be accessed by adding a Geometry Nodes Modifier.
The geometry node tree connected to a modifier is a Node Group. The geometry from the state before the modifier (the original geometry or the result of the previous modifier) will be passed to the Group Input node. Then the node group can operate on the geometry and pass an output to the Group Output node, where it will be passed to the next modifier.
Geometry nodes can modify different types of geometry:
The interface of the modifier is described in the Modifier page.
To expand Blender with node-group operators see the description in the Node-Based Tools page.