(1) A trigonometric function operating on angles in right-angled triangles. The tangent of an angle equals the ratio of the opposite edge to the adjacent edge.

(2) The unit vector describing the direction of a curve at a given point. Where a curve has a kink, the tangent is ambiguous.

(3) A plane whose z-axis is parallel to the normal vector of a surface at a given point. Where a surface has a crease, the tangent is ambiguous.