Gravity is another term widely used by brewers. This value indicates the amount of solids before fermentation. The vast majority of these solids are sugars, which are converted into carbonic acid and alcohol during fermentation. The gravity is a fairly accurate indication of how much alcohol the beer will ultimately contain.
Gravity is measured using the Plato scale. This value is used in the Netherlands to calculate the excise duty that brewers should pay. You may have noticed that on the labels of a Dutch beer bottle you always see a category designation (Cat.). For example, a pilsner is in Category 1. This means that it has a gravity of between 11 and 15.5 Plato. Heavy beers are classified in Category S and have more than 15.5 Plato.
Based on these figures you now have a good idea of what beer you are dealing with. Fortunately, that image is not complete - watching, smelling and, above all, tasting is still the best way to truly get to know a beer.