I mentioned it in another reply, but when I say filler, I refer to parts of the anime that are not in the manga. I always thought of filler as what felt like 90% of Naruto episodes, regardless of the content of the story or the episodes, if they aren't in the original manga they are filler.

That being said some of the filler is good, but I think most ends up being a complete throwaway in the overall life of a series.