Rosie the Riveter, Apple's 1984 comercial, the energizer bunny, Transformers. The amount of creativity that goes into advertising is both amazing and heart breaking. The creative part of advertising truely is creative, even if applied to such a dull task.
It's new to me. I did some research on Urban Dictionary (lol), and the definition for the usage of "Creative" as a noun was defined there as early as 2004. So I guess it's a usage that's been known for a quite some time.
"Creative" in the context of an ad means the image, video, text, etc. Basically, the ad content that the user will see.