PG100 Nicotine base
Here you order 100% PG (pure propylene glycol), designed to make your own e-juice for your e-cigarette. Be aware that neither aroma nor vegetable glycerine (VG) is added, which you would normally find in a standard e-juice.
In other words, 100% PG, or PG100 nicotine base in daily speech, is just one of the ingredients you need to mix your own e-juice.