A display rule is a set of display criteria which are processed on any view of a design. Display rules allow you to control the symbology, appearance, and display of design elements based on the property of an element, named group, view, model, reference, or file.

Display styles are associated with display rules. Each display rule contains a condition and its recommended action.

A display rule set consists of list of display rules. You can apply a display rule set to a display style from the Display Styles dialog.

You may also refer to the LEARNserver lecture What are Display Rules and Display Styles?