Heel and toe

From Trackpedia

This is an advanced form of downshifting where you slide your braking foot heel across to the throttle to blip it while under braking. The action for downshifting is basically brake, clutch in, blip throttle with brake foot heel while selecting next gear and releasing the clutch.

This helps spin the engine up and prevent the drive axle locking up because of mismatched engine RPMs. If this happened just before a corner then the car would likely spin.