Chern Class
A gadget defined for complex vector bundles. The Chern classes of a complex manifold are the Chern classes of its tangent bundle. The ith Chern class is an obstruction to the existence of (n-i+1) everywhere complex linearly independent vector fields on that vector bundle. The ith Chern class is in the (2i)th cohomology group of the base space.
See also
Chern Number, Obstruction, Pontryagin Class, Stiefel-Whitney ClassExplore with Wolfram|Alpha
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Weisstein, Eric W. "Chern Class." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/ChernClass.html