Spam is any post which does not add value to the discussion. Either it of itself is low quality, or the post has already been made and it is just a repetition of already discussed topics.
There is spam on most of the forum boards, with some more severe than others, having lots of spam mega threads, where the discussion is already moot but the thread drags on with repetitive replies, and the OP has already abandoned s post.
As has been mentioned, you can always report, spam, plagiarism, malwares to the mods for action.