An altitude of a triangle extends from one vertex to the opposite side, where this altitude is perpendicular to the opposite side. The term "altitude" is often interchanged with "height". Think of a tall mountain that has a lot of altitude, so it's got a lot of height.
Any triangle has 3 different altitudes (one per corner). For any triangle, those three altitudes always intersect at exactly one point: the <u>orthocenter</u>. This is one of the many centers of a triangle. Other centers are the centroid, incenter, and circumcenter.
