Sentence:  One day , Ching had told him ( smiling , patting him on the <WSD>back</WSD> ) as they walked to the weekly conference of squad leaders , `` Keep it up , your squad is good , one of the best , keep it up , keep up the good work '' . 
Meaning of the word marked with <WSD> tags:  the posterior part of a human (or animal) body from the neck to the end of the spine