Dark beers are a style that classifies beers by color. The fact is that a double and brown beer, are also a dark beers. This gives a limit to the categorization of beers without protecteing the styles by A.O.C or I.G.P.
Generally dark beers are included in everything that is not classified as abbey beer, even if this is not entirely true. You have to be careful with the label of 'abbey beer', because only two conditions must be met.
A third of the malt must come from monastic harvests (the monks produce a third of the barley on the Belgian market, which is not a problem) and the denomination of the abbey must have existed (which in Belgium is not complicated either). In fact, if we remove the second condition, we see that all Belgian beers could be labeled as 'abbey beer'.
Dark beers are a category of beer that is determined by their color. Generally these are abbey beers but the ‘double’ classification is more general today.
These beers are also less sweet and they have a slightly toasted aftertaste. The degree of alcohol is not a reference to be classified in this family.