Via

A via that spans and connects from the top layer (red) to the bottom layer (blue),
and also connects to one internal power plane (green).

A via is a primitive design object. It is used to form a vertical electrical connection between two or more electrical layers of a PCB. Vias are a three-dimensional object, having a barrel-shaped body in the Z-plane, with a flat ring on each (horizontal) copper layer. The body of the via is formed when the board is drilled and through-plated during fabrication. In the X and Y planes, vias are circular, like round pads. The key difference between a via and a pad is that as well as being able to span all layers of the board (top to bottom), a via can also span from a surface layer to an internal layer, or between two internal layers.