The informant spoke on condition of anonymity (=in return for his name not being mentioned) . 提供消息的人在要求不透露姓名的情况下说了话。
the bustle and anonymity of a big city (=where people do not know each other) 大城市的繁忙和人们相互间的陌生
the anonymity of the airport hotel 机场酒店的毫无特色