Wikipedia
A-segment
The A-segment is a car classification defined by the European Commission as the first segment in the European market car classification (mini cars). It is a significant niche in Europe with 10.4% market share in 2015.
In recent years, the segment opened to premium cars with success, like the Mini and the Fiat 500. Vauxhall/ Opel entered the segment with a premium model, the Adam, in the autumn of 2013. Vauxhall/Opel have had a presence in the A-segment since the launch of its Agila in 2000.
The New York Times described the segment in 2012, saying "today’s small cars actually span three main segments in the global vehicle market". A-segment cars (currently only 0.8% of US market) are dominated by European models Mini and Fiat 500.