I consider 100,000 pageviews a month easy because I can achieve that number organically (without paying for traffic) within a few months.

My niche is probably a bit easier than some others, though.

I also consider it easy in comparison to the fact that it took me 2 1/2 years to get to 600,000 a month when I first started. I could probably do 600,000 organically in half the time now.