Sentence:  Because only <WSD>ellipsoids</WSD> of rotation have been adopted in practical geodesy and surveying and triaxial <WSD>ellipsoids</WSD> have been limited to theoretical studies, we will use the term <WSD>"ellipsoid</WSD>" for brevity to mean <WSD>ellipsoid</WSD> of rotation. 
Meaning of the word marked with <WSD> tags:  A surface, all of whose cross sections are elliptic or circular (including the sphere), that generalises the ellipse and in Cartesian coordinates ("x, y, z") is a quadric with equation "x2/a2" + "y2/b2" + "z2/c2" = 0.