What exactly is “harassment” anyway?

Like, when I wrote that stuff yesterday, I was thinking of it as any kind of statements really intended to cause someone harm. The way Seebs was talking, though, it sounded like she was exclusively referring to aggression that is illegal. And then you have stuff like Anita Sarkeesian’s compilation of all the harassment she received in a single week, which includes every instance of “fuck you” and even a person saying “you’re not being harassed, people are disagreeing with you” - which is verifiably false, but only harassment insofar as it denies harassment is occurring.

There are definitely multiple definitions at play here, both when people describe their own experiences and interpret the experiences of others. Qualitative descriptions are one thing, but since the trend seems to be dealing with these things quantitatively, some kind of operational definition is necessary, and I’m actually pretty curious what you guys think.

What is harassment? What “tiers” of it exist? And, of course, where is the cutoff point between it and criticism (which can, in the right context, cause someone harm)?