##### Wiktionary

**diffeomorphism**

n. (context mathematics English) A differentiable homeomorphism (with differentiable inverse) between differentiable manifolds.

##### Wikipedia

**Diffeomorphism**

In mathematics, a **diffeomorphism** is an isomorphism of smooth manifolds. It is an invertible function that maps one differentiable manifold to another such that both the function and its inverse are smooth.