Can be used as a noun or verb.
Noun form = illegitimate behavior
Verb form = typically accompanied with the word "throw" or "throwing," as in to "throw someone shade" meaning to act shady, fake, or funny around or towards them.
Person 1: They went to the club and ain't even invite us!
Person 2: Shade!
My man been throwing me shade because I haven't been around as much.