Two open manifolds 
and 
are cobordant if there exists a manifold
with boundary 
such that an acceptable restrictive relationship holds.
Cobordant Manifold
See also
Bordism, h-Cobordism Theorem, Morse TheoryExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Cobordant Manifold." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/CobordantManifold.html