In geometry, an essential manifold is a special type of closed manifold.
The notion was first introduced explicitly by Mikhail Gromov.
[1] A closed manifold M is called essential if its fundamental class [M] defines a nonzero element in the homology of its fundamental group π, or more precisely in the homology of the corresponding Eilenberg–MacLane space K(π, 1), via the natural homomorphism where n is the dimension of M. Here the fundamental class is taken in homology with integer coefficients if the manifold is orientable, and in coefficients modulo 2, otherwise.
This Riemannian geometry-related article is a stub.
You can help Wikipedia by expanding it.