Source : Webster's Revised Unabridged Dictionary (1913)

Tailboard \Tail"board`\, n.
   The board at the rear end of a cart or wagon, which can be
   removed or let down, for convenience in loading or unloading.

Source : WordNet®

tailboard
     n : a gate at the rear of a vehicle; can be lowered for loading
         [syn: {tailgate}]