What is the meaning of Layman?

Layperson, someone who is not an ordained cleric or member of the clergy.

Someone who is not a professional in a given field.

A common person.

A person who is untrained or lacks knowledge of a subject.

Lay-sister or lay-brother, person received into a convent of monks, following the vows, but not being member of the order.

Source: wiktionary.org