Given four points, A, B, C, and H, let H be the orthocenter of Δ A B C. Then A is the orthocenter Δ H B C, B is the orthocenter of Δ H A C, and C is the orthocenter of Δ H A B. The configuration A B C H is called an orthocentric quadrangle.

orthocenter | orthocentric quadrilateral | orthocentric system