Terrorism, according to Wikipedia, is "the use of violence against non-combatants to achieve political or ideological aims."
Hamas is doing that, see examples.
I frankly don't see, whatever its goals, how systematically attacking civilians can not be terrorism. (Since Native Americans to my knowledge don't do that, I wouldn't call them terrorists, no).
This definition fits israel just as well or better, do you typically refer to it as a terror org?