Polygon

Altitude - the perpendicular distance from a vertex of a figure such as
a triangle,
to the base which is the side opposite the vertex.

Altitude of a Polygon - the line segment drawn from any vertex of a
polygon perpendicular to the opposite side.

Altitude of a Triangle - the perpendicular segment from a vertex to

the line containing the opposite side


Note: Pls. click the video about Pythagorean Theorem view this in full screen.