Wisdom teeth are the third molar teeth. They are located all the way back in the jaw, and tend to come in some time between the ages of 16 and 25, if they come in at all. For many people their wisdom teeth coming in impacts other teeth, requiring surgery to remove the wisdom teeth to allow their jaw to remain healthy. Generally infants form a first set of teeth, commonly called baby teeth, which eventually fall out and give way to the adult teeth, that will remain until old age. Wisdom Teeth come quite a bit after the full set of adult teeth have grown.
Wisdom teeth are so named because of the time they appear, generally in the late teens or early twenties, when people are presumably "wiser" than as a child, when the other teeth erupt.