What is the shape of a cylinder's base?

The base of a cylinder is best described as a circle. A cylinder is defined as a three-dimensional geometric figure with two parallel bases that are congruent circles. The circular shape allows the cylinder to have uniform cross-sections along its height. This characteristic is fundamental to the definition of a cylinder and distinguishes it from other geometric shapes, such as prisms, which have polygonal bases. Recognizing that the base is circular is crucial for understanding the properties and formulas related to cylinders, such as calculating the volume and surface area.