solid angle

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An angle having a value equal to the area on a sphere subtended by a surface, divided by the square of the radius of that sphere. Solid angles are measured in steradians.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun geometry The three-dimensional analog of an angle, equivalent to the area of that portion of the surface a unit sphere that it subtends.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an angle formed by three or more planes intersecting at a common point (the vertex)