base oil, lubricant, Group V - are used primarily in the creation of oil additives.

Esters and polyolesters are both common Group V base oils used in the formulation of oil additives.

Group V oils are generally not used as base oils themselves, but add beneficial properties to other base oils. 

Note that the additives referred to in the Group V description are not aftermarket type oil additives. The additives referred to are used in the chemical engineering and blending of motor oils and other lubricating oils by the specific oil company that produces the finished product.