A doughnut shape with 2 holes
The theorem of classification of the surfaces states that any compact, connected, orientable surface without boundary can be related to a standard surface. We can visualize these standard surfaces as spheres with some handles attached or, otherwise, as doughnuts with a certain number of holes. The figure shows an example of doughnut with 2 holes; we can easily imagine donuts with a greater or smaller number of holes.
The image belongs to the sections...:
The double torus (Topology)
Standard surfaces (Topology)