a swing bridge is a bridge that can be moved either clockwise or counterclockwise to allow for ship traffic pass by without any overhead obstructions.

A moveable bridge, being pivoted in the middle to move out of the way of river traffic.

A swing bridge is a bridge that has as its primary structural support a vertical locating pin and support ring at or near to its center, about which it can then pivot horizontally as shown in the animated illustration below. Small swing bridges as found over canals may be pivoted only at one end, opening as would a gate, but require substantial underground structure to support the pivot.