'2+2' is a term usually applied to a car with a closely-coupled coupe body; it signifies that the back seats are suitable for occasional use only.
'2+0' is the description Aston Martin applies to its strictly two-seat V8 Vantage. Hadn't come across that one before.
Which reminds me – the seating configuration is one of the main differences between the DB9 (2+2) and the V8 Vantage (2+0). The back seats on the DB9 don't look like much and the legroom offered is very limited too. But the small rear compartment of the DB9 has a remarkable Tardis-like ability to accommodate tall passengers, or at least that's what I found during the Verdict test of the Vantage's larger sister a couple of years ago, when some very large people indeed managed to insinuate themselves into the tiny space available for the glorious privilege of being taken for a spin in an Aston.