The Node Graph Frame is a organizational feature in the Node Graph Viewport that allows you to highlight nodes using a frame with a title and color.
The Node Graph Frame can be created from the Nodes List window:
In the Node Graph viewport right click on an empty space. The Nodes List window is displayed.
In the text field type Node Graph Frame.
Double click the Node Graph Frame item in the list. A default node graph frame is added to the viewport.
Drag the sides of the node graph frame to cover the background of the nodes you want to highlight.
Right click the left-top corner of the node graph frame to display the Frame Properties window. Edit the properties of the node graph frame.
Click ok to close the window.