Osama was the leader of a well organized group who carried out attacks and campaigns based on an overall plan to induce terror and thereby achieve a political goal.

So yes, Osama was a terrorist.

As was George W.Bush and many members of the US government and military hierarchy who also planned and orchestrated campaigns aimed at terrorizing local populations in order to achieve political goals, not only in Iraq and Afghanistan, but in the US as well.

James Holmes is a lone man, who acted on his own, for no known political reasons, with no known goals and with no plans to continue harming people (since he gave himself up to police). He is as much a terrorist as a guy who kills his wife for having an affair.