Orthogonality

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In mathematics, orthogonality is the generalization of the geometric notion of perpendicularity. Whereas perpendicular is typically followed by to when relating two lines to one another (e.g., "line A is perpendicular to line B"),^[1] orthogonal is commonly used without to (e.g., "orthogonal lines A and B").^[2]

Orthogonality is also used with various meanings that are often weakly related or not related at all with the mathematical meanings.