We currently have a tag mate with 195 questions and the following description:
MATE is a desktop environment based on Gnome 2.
We also the tag mate-desktop with 5 questions and the following description:
mate-desktop is an alternative desktop environment to traditional GNOME . It uses gtk+ components and has less memory power usage than GNOME uses. Most of the tools are named in spanish for e.g. caja which is supposed to be mean 'box' in Spanish and so on and so forth.
As far as I can tell, both tags are about one and the same desktop environment, namely the one produced by the MATE Team. For this reason, I suggest that mate-desktop be turned into a synonym for mate. (The description for mate can be expanded, but that doesn't require a meta question.)