(1) I'd rephrase your question slightly: "I'd like to know what "gimmick" stands for in this sentence." (Because you began the sentence with, "I'd like to know," you don't need the "does" part of the question). (2) A gimmick is something that seems appealing on the surface, but really is not that useful or of high quality. It is probably most frequently used when referring to some technology; if a technology proves to be more flashy than it is useful, we'd call it a gimmick If social media were a gimmick, it would seem really appealing to use it for marketing, but it wouldn't produce any more sales. In this case, the sentence is saying that social media is *not* a gimmick, and therefore will be at least somewhat useful for marketing.