The propensity or ability to think, act, or form opinions without outside influence. It is often used (humorously) to describe an inanimate object that cannot be controlled by its owner. I tried to tell him that wasn't the best decision to make under those circumstances, but you know he has a mind of his own, and he did it anyway. I swear, my vacuum has a mind of its own! It turns on in the middle of the night when we're all asleep!