Of course there are accidental discharges. Yes almost always the trigger must be pulled (though there have been cases where it wasn't). Accidental refers to the intent to discharge the weapon.

Out on the range a friend of mine who didn't know what he was doing pulled the trigger while a man was down the line. What do you call that? Is that an accidental discharge? Are we talking semantics? What would you call it then? A unintentional near miss?

And criminally speaking, intent matters. That is not to say that a lack of intent will get you off or make something excusable, it doesn't. Intent can make the difference between bars and a needle.