User blog comment:HiddenVale/Enlighten me, please/@comment--20121004050704

Wikia's Terms of Use states that one may not "Post, upload, transmit, share, or store unsolicited or unauthorized advertising, solicitations, "spam", or any other type of unauthorized solicitation", so through context one can begin to draw some conclusions.

Wikipedia's definition of Spam is also pretty fleshed out.

Though I also agree User452's list covers some good examples of what spam is. Essentially what it comes down is to is intent - is the intent of the user posting to disrupt the flow and stability of a wiki for the purpose of furthering a different product/service/wiki, etc., etc. "Spamming" in the chat context can refer to simply adding gibberish over and over again or posting about a topic a user has been asked repeatedly to stop posting.