What is diameter?

Diameter is a straight line segment which passes through the center of a circle or a sphere, and its endpoints lie on the circumference of the circle or the surface of the sphere. It is twice the length of the radius of the circle or sphere. The diameter is a fundamental property of circles and spheres, and it is used to calculate many other geometric properties, such as the area, circumference, volume, and surface area. In many practical applications, the diameter represents the size of a circular or spherical object, such as a wheel, a pipe, a ball, or a planet. The diameter is measured in units of length, such as meters, feet, or inches, depending on the context.