Sentence:  To assume the correct position for the posting <WSD>trot</WSD>, first walk, with the body inclined forward in a posting position. Then put the horse into a slow or sitting <WSD>trot</WSD> at six miles an hour. "Do not post." 
Meaning of the word marked with <WSD> tags:  A gait of a four-legged animal between walk and canter, a diagonal gait (in which diagonally opposite pairs of legs move together).