What is a three-dimensional rectangle called?

A three-dimensional rectangle is called a cuboid. A cuboid is defined as a closed box that is composed of six rectangular faces joined at right angles. The rectangles on opposite faces of the cuboid are identical to each other.

A cuboid in which all the edges are the same length is called a cube, which could also be described as a three-dimensional square. Calculating the volume of a cuboid is accomplished by multiplying the three edge lengths together. The surface area of a cuboid is equal to the sum of the areas of the rectangles that make up each side.