It means to quit.This phrase comes from boxing. When a boxer is too beat up to continue, his coach throws a towel into the ring to signal that the fight is over. Note: Throw in the towel的意思是认输,来源于拳击比赛。当拳击手打不过对方,他的教练会抛一条毛巾入场,表示认输。 例:The company threw in the towel after losing all of its major customers. 公司丢了所有的主要客户之后只好举白旗认输了。