noun, maths a) a three-dimensional closed surface such that every point on the surface is equidistant from a given point, the centre b) the solid figure bounded by this surface or the space enclosed by it. Equation: (x–a)² + (y–b)² + (z–c)² = r², where r is the radius and (a, b, c) are the coordinates of the centre; surface area: 4πr²; volume: 4πr³/3

From Collins

©HarperCollins 2008. Collins English Dictionary definition of sphere