No, not mini-skateboarding with your fingers. That doesn’t even count as a sport. Real handboarding, also called handplaning, is surfing, or bodysurfing, with a miniature surfboard attached to one hand. Or sometimes two, depending on your style.
Using a handboard (or handplane) allows you to go higher and faster than regular body boarding and get points for being epically awesome. So if you like water sports, this is a pretty unique one, and cheap to get into. You can pick up a handboard on Amazon for around $35.