Every Widget has a number of resources. These control many features of the widget such as the foreground/background colours, size etc.. A particular widget will have specialised resources such as callback resources which define how the widget responds to an event etc..
Every Widget is documented in the Motif Reference Manual which gives a complete list of resources a particular widgets employs.
There is a hierarchy of resources (Fig 5) and a widget will inherit resources from a higher resource class.
Fig. 5 Widget Hierarchy
The levels of the hierarchy are: