Homotopy groups are examples of topological invariants: topologically equivalent spaces have the same homotopy groups. Roughly, the nth homotopy group of a topological space M expresses the inequivalent ways an n-sphere can be continuously mapped into M, regarding two such maps as equivalent if one can be continuously morphed into the other. The homotopy group with n=1 is called the fundamental group. This article introduces homotopy groups and the related concept of a covering space. A covering space E of M is like M but "unwrapped" so that E's fundamental group is only part of M's fundamental group.
