Affine connection, a connection on the tangent bundle of a differentiable manifold
Affine Coordinate System, a coordinate system that can be viewed as a Cartesian coordinate system where the axes have been placed so that they are not necessarily orthogonal to each other. See tensor.
Affine differential geometry, a geometry that studies differential invariants under the action of the special affine group
Affine gap penalty, the most widely used scoring function used for sequence alignment, especially in bioinformatics