flatness  
noun [ U ] uk/ˈflæt.nəs/ us/ˈflæt.nəs/
  (LEVEL QUALITY)      
  平坦
the quality of being level and without curved, high, or hollow parts
  The flatness of the desert was broken only by a few large piles of rocks. 沙漠看上去很是平坦,仅有几大堆石头点缀其中。 
   (NO EMOTION)      
 平淡;乏味
the fact that someone or something shows no emotion or interest
  All the critics remarked on the flatness of the performance. 所有的评论家都谈到这场表演平淡乏味。