Your question was posted under 3-Cushion Billiards, which is a game I've never played. But I'm answering you so that you get a quick acknowledgement and in case my games have the same standard about miscues.
"Miscue", by definition, means "by accident". If a shooter tries to get away with some trick method by disguising a shot as an accident (for example, finding a way to make the cue ball go sideways off the side of the cue), it is a serious foul and has more consequences than a standard foul. Beyond that, a miscue causes a foul only if the shot fails to achieve the standards of a legal shot, such as having the cue ball hit a legal ball, then driving any ball to a cushion (or pocket, which wouldn't happen in 3-Cushion). Again, I don't know which of the balls in 3-cushion make-up a legal shot.
The miscue isn't a foul in itself, but usually causes one. It is a foul to make a jump shot by purposely miscuing off the bottom of the cue ball, but I assume jump shots aren't used in 3-Cushion.
UPDATE: From USBA:
- Miscues are not a foul unless the player's ferrule or shaft touches the cue ball during the execution of the stroke. If a billiard is scored because of a miscued stroke, it shall be counted and turn continues (unless the miscue was a foul).
So, the shooter would have to totally miss the cue ball with his cue's tip, or the ball somehow bounced back to the side of the cue. I would say that totally missing the cue tip would, technically, not be a miscue!