Most sites have a niche. This forum's niche is internet marketing. I manage a site whose niche is "nz property investors" and another whose niche is "education for nz property investors" the niche of the first is pretty specific, the second even more so. These sites rely on targeted and repeat traffic rather than volume.
I do SEO and Cartoon SEO which caters for other "niches" Many people chase after the "latest trends" rather than becoming expert and an "authority" in a "niche"