Pg (propylene glycol) - the "flavor carrier" of
e-liquid. A secondary source of "throat hit", but not as strong as the nicotine concentration. Some people have a sensitivity or even an allergy to Pg.
Vg (vegetable glycerin) - the "vapor maker" of
e-liquid. Used as a sweeter in many food sources, and also as a skin emollient.
Pg and Vg are often used together in different ratios in
e-liquid. For example, a 50/50 pg/vg ratio.