A rhythmic up-and-down movement of your own body weight that generates fresh lift — with no wave, sail or kite involved. When you lose speed you reduce the load instead of pressing down.
Pumping is the skill that turns surf foiling into a discipline of its own: you link a dying wave to the next line of swell and stay airborne for minutes, far beyond the length of any single wave. The beginner's error is almost ironic — as speed drops, the reflex is to push the back foot down, when the right move is the opposite: take load off so the wing can rebuild lift. Mistake two is using too much force. The impulse comes from knees, hips and torso together, and small, well-timed movements achieve more than powerful, badly-timed ones. Learn the rhythm in calm water before you need it in the line-up. What often gets missed: pumping carries you further from your starting point than you plan. Keep the way back in mind and stop as soon as your legs tire — tired legs mean worse timing, and worse timing means more falls onto your own foil.