Use of violence: The suspect used a Glock 19 semiautomatic handgun to kill six individuals.
Non-State Actor: Jared Loughner, the suspect in the case who has now been charged, is not affiliated with any government.
Against Civilians: The following civilians were killed in the attack:
Christina Taylor Green, 9
Gabe Zimmerman, 30
Dorothy Morris, 76
Dorwin Stoddard, 76
Phyllis Schnek, 79
U.S. District Judge John M. Roll, 63, was also killed.
Congresswoman Giffords is in critical condition.
The targeting of a government official falls within the category of assassination, which is a different subset of political violence than terrorism because its victims are agents of the state, not purely civilians. However, civilians were almost certainly a target in this attack in addition to Congresswoman Giffords herself, and Judge Roll.
Political End: Loughner's videos are highly political in nature, speaking to anti-government and fundamentalist themes. His choice of Rep. Giffords appears to be premeditated. Additionally, the government has responded to the event. Many representatives (one example here) have said they will have extra security at upcoming events.
A lingering question is Loughner's mental health. The debate over whether a mentally ill individual can have anti-government "intentions" is one which is not likely to be solved in the near future. But Loughner's targets were not chosen out of a sense of personal wrongdoing but because they held political value, a judgement made by Loughner himself.
In summation: Given that Jared Loughner is not insane, the targeting of Judge Roll is an assassination. The targeting of Congresswoman Giffords is an attempted assassination. The targeting of 5 civilians by Jared Loughner for the political end of destabilizing the government of the United States is lone-actor terrorism.