simply-connected space
A topological space that is path-connected and has a trivial fundamental group; every loop can be continuously shrunk to a point.
A sphere is an example of a simply-connected space.
A torus is not a simply-connected space.
連結空間 (connected space) only requires that the space cannot be split into two disjoint non-empty open sets; 単連結空間 additionally requires that every loop is contractible.
Compound of 単 (simple) + 連結 (connection) + 空間 (space), a direct translation of the English mathematical term 'simply-connected space'.