A board originally meant to emulate the feeling of surfing on land. Typically longer than a normal skateboard, but not necessarily. Longboards are for people who want a smooth, chill ride. Also, they are fantastic means of transportation in urban areas where bikes are inconvenient and commonly get stolen. They are far superior to normal skateboards, which offer much less control and a much bumpier ride.
Skateboarder: Dude, just pulled some kickflip 720 grind spins back at the park on my skateboard.
Longboarder: That's very nice man. I just enjoyed the warm rays and calming breeze on the way over here on my longboard.