Display Flag for Network Backdrop and Viewer Panes
If a Network Editor pane has the backdrop display option enabled, then the OPs of that type with their display flags on will be shown in the backdrop of the editing pane. The network will 'float' on top. Backdrop display is enabled using the network editor's right-click menu, Display > Backdrop TOPs (or Backdrop CHOPs/Backdrop Geometry).
Display Flag for Geometry and Camera Viewers
The same Display flag on 3D components is used to select objects to view in a Camera component, and in the parent's viewer.
Any of the procedural data operators. OPs do all the work in TouchDesigner. They "cook" and output data to other OPs, which ultimately result in new images, data and audio being generated. See Node.