A diameter is a line segment passing through the center of a circle or sphere with both its endpoints on the circle or sphere. It is the longest distance between two points of the circle or sphere; more generally the diameter of a set is the longest distance between two of its points.
Other topics related to the diameter of circles and sets include: Angular diameter, how large a circle or sphere appears in a field of view Diameter (computational geometry), the problem of computing the longest distance between two of given points or of the points in a polygon Diameter (graph theory), the longest distance between two vertices of a graph Diameter (group theory), the maximum diameter of a Cayley graph of the group Equivalent diameter, the diameter of a circle or sphere with the same area, perimeter, or volume as another object Hydraulic diameter, the equivalent diameter of a tube or channel for fluids Kinetic diameter, a measure of particles in a gas related to the mean free path Kinetic diameter (data), the algorithmic problem of keeping track of the diameter of a moving point set Link diameter of a polygon, the number of segments needed to connect each two points in the polygon by a polygonal chain that stays inside the polygon List of gear nomenclature#Inside diameter, a measurement of the size of a gear Sauter mean diameter, the equivalent diameter of a particle Screw thread#Diameters, several measurements of a threaded screw or bolt Semidiameter, half of the diameter of a circle or sphere
Diameter may also refer to: Diameter (protocol), a computer communication protocol for authentication, authorization, and accounting
See also Demeter (disambiguation)