Pushforward (differential)

In differential geometry, pushforward is a linear approximation of smooth maps (formulating manifold) on tangent spaces. Suppose that φ : M → N {\displaystyle \varphi \colon M\to N} is a smooth map between smooth manifolds; then the differential of φ {\displaystyle \varphi } at a point x {\displaystyle x} , denoted d φ x {\displaystyle \mathrm {d} \varphi _{x}} , is, in some sense, the best linear approximation of φ {\displaystyle \varphi } near x {\displaystyle x} .

Source: Wikipedia — Pushforward (differential) (CC BY-SA 4.0)