Sentence:  The simplest example of a <WSD>foliation</WSD> is provided by a single submersion "F" : "M" → "N", "M" and "N" being manifolds. 
Meaning of the word marked with <WSD> tags:  A set of submanifolds of a given manifold, each of which is of lower dimension than it, but which, taken together, are coextensive with it.