osculating plane
plane in a Euclidean space or affine space which meets a submanifold at a point in such a way as to have a second order of contact at the point
en-GB/ɒskjʊleɪtɪŋ ˈpleɪn/
plane in a Euclidean space or affine space which meets a submanifold at a point in such a way as to have a second order of contact at the point