the basic unit of solid angular measure in the SI system, equal to the solid angle subtended at the center of a sphere by an area, on its surface, that is equal to the square of its radius: one sphere equals 4π steradians: abbrev. sr
ste(reo)- + radian
See steradian in American Heritage Dictionary 4
noun Abbr. sr
A unit of measure equal to the solid angle subtended at the center of a sphere by an area on the surface of the sphere that is equal to the radius squared: The total solid angle of a sphere is 4π steradians. See Table at measurement.