The altitudes of a triangle intersect at a common point known as the orthocenter.

The location of the orthocenter depends on the type of the triangle. In an acute triangle just like the one below, the orthocenter is found inside the triangle.

orthocenter of acute triangle

If it is a right triangle, the orthocenter is found on the triangle itself.

orthocenter of right triangle

If it is an obtuse triangle, the orthocenter is found outside the triangle.

orthocenter of an obtuse triangle