1. 外行；门外汉
    A layman is a person who is not trained, qualified, or experienced in a particular subject or activity.

    e.g. The mere mention of the words 'heart failure', can conjure up, to the layman, the prospect of imminent death...
           一提“心脏衰竭”四字，外行人就联想到命不久矣的情景。
    e.g. There are basically two types called, in layman's terms, blue and white asbestos.
           基本上有两种，用外行话说就是青石棉和白石棉。

2. （基督教中的）平信徒，在俗教徒
    A layman is a man who is involved with the Christian church but is not a member of the clergy or a monk.

layman的意思

    e.g. In 1932, one Boston layman wrote to Archbishop William O'Connell in support of Father Coughlin.
           1932年，波士顿一名平信徒致函大主教威廉·奥康奈尔，声援库格林神父。