Layman

The term "layman" originated from the use of the term laity, but over the centuries, changed definition to mean a person who is a non-expert in a given field of knowledge.

The concept of describing something in layman’s terms has come into wide use in the English speaking world. To put something in layman’s terms is to describe a complex or technical issue using words and terms that the average individual (someone without professional training in the subject area) can understand, so that they may comprehend the issue to some degree.

An explicitly gender-neutral version of the word is layperson.