nLab simple foliation

A regular foliation $\mathcal{P} \hookrightarrow T X$ is called simple if the leaf space $X/\mathcal{P}$ is a smooth manifold and the quotient projection $X \to X/\mathcal{P}$ is a surjective submersion.

Conversely, a simple foliation is a foliation by leaves of a surjective submersion.