ABV means Alcohol By Volume. Alcohol by volume (ABV) simply represents what portion of the total volume of liquid is alcohol. To determine the ABV of a beer, a brewer typically uses what's called a hydrometer, which is an instrument that aids in measuring the density of liquid in relation to water (it essentially free-floats in a cylinder or liquid). The hydrometer will be calibrated to read 1.000 in water (at 60°F), and the denser the liquid (example: add sugar to the liquid), the higher the hydrometer Reading.