A Shortfill e-liquid is basically a large bottle which is only part-filled with 0mg nicotine e-liquid. This bottle has enough space to pour in one or two 10ml bottles of high-strength nicotine e-liquid, to get the desired strength.
Shortfills work best for anyone who wants to stock up e-juice but save money as well. They are known to have the low price which makes them perfect for heavy vapers or those using juice-hungry sub-ohm tanks.
All Shortfill e-liquids are made from nicotine-free e-liquid, this means that they are limited to the lower nicotine strengths. If you use 6mg e-liquid or lower, then a shortfill e-liquid is all you need.