A facet is one section (plane or surface) of a multi-sectioned roof that is over 4 square feet.
For example, a standard up-and-over roof with 2 sections has 2 facets:
The same roof with a dormer on it would have 4 facets:
Here's an example of a roof that has 10 facets:
Where is this information in the measurement PDF?
You can see the total number of roof facets (RF) and their combined total area in the table on the Roof Summary page. However, we include additional details on the Roof Facets page. There, you'll find a breakdown of each roof facet's area, pitch and location on the roof diagram: