Which of the following terms best describes a two-dimensional geometric shape?

A two-dimensional geometric shape is characterized by having only length and width, while lacking depth. Among the given options, a triangle is the only shape that fits this definition, as it exists entirely in a flat plane and is defined by three straight sides and three angles.

A cylinder, pyramid, and sphere are all three-dimensional shapes. Each of these has depth in addition to length and width, which is why they do not qualify as two-dimensional geometric shapes. Understanding the differences between two-dimensional and three-dimensional figures is crucial in geometry, as it affects how we calculate area and volume and how we visualize spatial relationships.