Firstly, PG stands for Propylene glycol. This is an organic compound in the form of a thick, colourless liquid with a slightly sweet taste. Propylene glycol is added to e-liquids as a thickener and base. Its presence in e-liquid provides you with that “throat hit” which is usually linked to the sensation of smoking.
Secondly, VG stands for vegetable glycerine. It is very similar to propylene glycol in that it is odourless, colourless and has a faint sweet flavour. It is used to thicken the consistency of e-liquid, which in turn creates the dense vapour clouds associated with vaping.