If two pairs of opposite sides of a complete quadrilateral are pairs of perpendicular lines, the quadrilateral is said to be orthocentric. In such a case, the remaining sides are also perpendicular.
Orthocentric Quadrilateral
See also
Orthocentric Quadrangle, Orthocentric SystemExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Orthocentric Quadrilateral." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/OrthocentricQuadrilateral.html