A Window Decor defines how a window looks. There are two different meanings of Window Decor that could get used.

The collection of all the different things that can be configured to affect the look of a window.
The Decor definition (see AddToDecor) which is a wrapper for some of the options, namely ButtonStyle, TitleStyle and BorderStyle.
https://www.fvwm.org/Wiki/Config/Decor/
