There are two Intrinsic notions of boundary for non-collapsed RCD (ncRCD in short) spaces and the regularity and topology of both notions are relatively well understood. On the other hand, there is also a notion of topological boundary when a ncRCD(K,N) space contains a ncRCD(K,N) subspace, which is extrinsic. In this talk, I will present a recent study on the relation between the extrinsic and intrinsic notions of boundary. For Alexandrov spaces, an invariance of domain theorem is employed to get some stronger results. This is joint work with Vitali Kapovitch.