A Recovery Boost is a technique featured in every Mario Kart game since Mario Kart 64. After falling off the track or going out of bounds, Lakitu will fish you out and drop you back on the course. If you press the accelerate button as soon as you hit the ground after being dropped, you will receive a small boost to get you going, about the same as a mini-turbo. This is very helpful to avoid losing further time after a recovery since you would need to accelerate from zero, which can take a while for low acceleration karts.