Trail braking is an advanced riding technique of motorcycle riders which requires professional training, and it is also used in car racing, meaning to continue to brake into a turn.
It is the action of dragging brakes when cornering a motorcycle. The purpose of trail braking is to stabilize the the bike, give more traction and also make the rider ready for unpredictable circumstances.
As a motorcycle rider approaches a turn they apply both front and rear brakes to slow down.
Then when the correct speed is achieved, they partially release the brakes pressure, as to keep dragging the brakes throughout the turn.
As they drag the brakes into the turn, they should open the throttle a little to keep the bike from slowing down, which is known as "maintenance throttle". This will give more traction as the tires are forced into the pavement and also stabilize the frame of the bike.