When vertices are selected, Detach separates any selected vertex that is shared by multiple faces into multiple vertices depending on the number of faces the vertex shares. The edges of the faces associated with the vertex also become unshared as a result.
Note: Detach ignores any vertices that are not shared.
When edges are selected, Detach separates the selected edges into two overlapping edges. If you perform a Detach operation over a path of edges, the vertices along that path are also separated along that path. The vertices at the ends of each selection remain attached to both of the new edges or edge paths.
If both vertices and edges are selected, Detach defaults to the same behavior as when only vertices are selected.
Note: You can access Detach from the marking menu by clicking 
+ 
when Edge mode is active.
+ when Edge mode is active.