Ellipsoid is a family of surfaces that can be described by this equation: “(x/a)^2 + (y/b)^2 + (z/c)^2 == 1”. It is called ellipsoid because the cross section alone the axes of the surface are ellipses, and the equation's form is the 3D analogue of the equation for ellipses.
Parametric formula:
a = 1; b = 2; c = 2.6; ParametricPlot3D[{a*Cos@[u]*Sin@[v], b*Sin@[u]*Sin@[v], c*Cos@[v]}, {u, 0, π}, {v, 0, 2*π}]
Other algebaric surfaces that has cross-sections of conic sections are: ellipsoid, paraboloid, hyperbolic paraboloid, hyperboloid of one sheet, hyperboloid of two sheets.