plain作形容词时有“简单、朴素”之意。而英语的世界里，Jane这个名字也很普通。plain-Jane用来形容妹纸“相貌平平”、“不起眼” 。

【例句】
Studies have shown that they are more likely to be promoted than their plain-Jane colleagues.
研究表明，她们总是比相貌平平的同事更容易获得升职机会。

She is an average-looking girl.
她是一个长相很普通的妹纸。