"Terrorism" means more than just doing very bad things. Terrorism is violence against innocent people in order to further a cause.

Both Adam Lanza and the Beslan terrorists[1] killed lots of kids. But only the Beslan killers were terrorists. They hoped to further the goal of Chechen independence from Russia. Lanza was just a homicidal maniac.

[1] http://en.wikipedia.org/wiki/Beslan_school_hostage_crisis