A relation between Compact boundaryless Manifolds (also called closed Manifolds). Two closed Manifolds are bordant Iff their disjoint union is the boundary of a compact -Manifold. Roughly, two Manifolds are bordant if together they form the boundary of a Manifold. The word bordism is now used in place of the original term Cobordism.
Budney, R. ``The Bordism Project.''