In topology and related branches of mathematics, a connected space is a topological space that cannot be represented as the union of two or more disjoint non-empty open subsets. Connectedness is one of the principal topological properties that distinguish topological spaces.
A subset of a topological space X {\displaystyle X} is a connected set if it is a connected space when viewed as a subspace of X {\displaystyle X} .
Some related but stronger conditions are path connected, simply connected, and n {\displaystyle n} -connected. Another related notion is locally connected, which neither implies nor follows from connectedness.