Which four-sided shape is always categorized as a rectangle?

The question asks which four-sided shape is always categorized as a rectangle. The correct answer is the square.

A square is defined as a specific type of rectangle that not only has all right angles (just like a rectangle) but also has all four sides of equal length. This means that every property applicable to rectangles applies to squares as well, including having opposite sides that are equal and parallel. Therefore, a square meets all the criteria to be classified as a rectangle, while also having additional constraints that make it a unique subset within that category.

In contrast, while a rectangle is a broader category that includes all shapes with four right angles, a parallelogram can have sides of varying lengths as long as opposite sides are equal and parallel, and does not necessarily have the right angles required for rectangle categorization. A trapezoid, meanwhile, has only one pair of parallel sides and does not conform to the defining properties of rectangles.