What term refers to a U-shaped section of rope with parallel sides?

The term that refers to a U-shaped section of rope with parallel sides is known as a bight. A bight is formed when a length of rope is doubled back on itself without crossing, creating a section of the rope that is not under tension. This characteristic makes the bight useful for various applications in rope rescue operations, such as creating anchors or forming loops for securing gear.

In contrast, a loop typically refers to a bight that has been crossed over and secured, often used in knot tying where both ends of the rope may be used to secure the loop. A hitch involves tying the rope to an object, thereby securing it in place, and does not represent the specific formation of rope described in the question. The running end refers to the part of the rope that is free and can be pulled or moved, which is not applicable in describing the U-shaped formation presented in the question.