it's called, "backing into the corner". He's sliding in underthe brakes and squaring off the cornewr before spinning the tire up through the corner.
Some of it looks like from him braking but a lot just seems to be his tires losing traction from him leaning? Cuz its like he is leaned all the way over then it slips some and he catches himself. I dunno tho:O
Thats called "throttle control", he's taking the tires close to their traction limits and using the throttle to spin up the tire throughout the corner.
Basically, he's drifting a bike or "powersliding"