A "fastback profile" refers to a design or shape of a vehicle, often used to describe a car with a sleek and sloping roofline that extends smoothly to the rear, creating a streamlined appearance. Full definition
The arcing roofline descends almost seamlessly into the C - pillar and, subsequently, the rear decklid, imparting the CLS with a unique fastback profile. (kbb.com)
Its signature roofline and shapely greenhouse give the car a flowing, uninterrupted form that extends rearward to a sleek fastback profile. (kbb.com)
Perhaps most importantly, the RF's slick fastback profile just looks fantastic, sweeping from the A-pillar almost all the way to the edge of the rear decklid in one smooth curve. (cnet.com)