Two surfaces are called orthogonal if it is perpendicular at a point of intersection if their normal lines are perpendicular at that point.
Surface families that are mutually orthogonal. In three dimensions, up to three families of surfaces can be orthogonal.
Orthogonal planes are the most basic example of three orthogonal surfaces in three dimensions, but three confocal conic surfaces are also mutually orthogonal.
Thus, the correct option is orthogonal
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