The phrase "double clutch" means to shift gears twice when driving a manual transmission car. It is done to smoothly change gears and match the engine speed when downshifting. Full definition
The engine will be mated to a seven speed double clutch transmission. (thesupercars.org)
The engine has been tailored to the hybrid application and is combined with a six - speed double clutch transmission to enable a more dynamic driving experience than some other hybrids. (greencarcongress.com)
What's missing is the 7 speed double clutch gearbox option. (bmwblog.com)