Many good answers but RDY4WAR had the first correct and complete answer.
Group V Naphthenic oils are sometimes called "Pale Oils" because of their pale color and are rich in cyclo-parrafins.
Cyclo-parrafins (also called "naphthenes") are saturated cyclic hydrocarbons of the general formula CnH2n, i.e, a hydrocarbon with a molecule containing a ring (cyclic) of carbon atoms joined by single bonds.
They are rich in aromatics which gives them a solvency advantage for certain additives.
Their low paraffin (a flammable, whitish, translucent, waxy solid consisting of a mixture of saturated hydrocarbons) content gives them an inherently low pour point.
But they also have a relatively low VI and their lubricating performance and oxidation stability are poor.
Their applications are in transformer oils, additive solvents, spray cans as the solvents for lubes and rust preventives, and other specialty applications.