quintile       
noun [ C ] uk/ˈkwɪn.taɪl/ us/ˈkwɪn.taɪl/
 mathematics specialized五分之一 
one of five equal measurements that a set of things can be divided into
  Those in the bottom quintile are the 20 percent with the lowest incomes. 处于最底层五分之一的人也就是收入最低的20%。 
 Compare: quartile