Lay originates from the
word "
laicus" in
Latin, which comes from
Greek "
laos" (
people). It
means a
person who is not a
cleric (
member of the
clergy).
In a more
contemporary meaning, a
person who's not an
expert, or not
familiar enough with a given
subject, is a
lay person to that
particular subject.
We're all lay people to most subjects, and some of us even are
experts in a
few areas.
Thanks to whizkid for the origins.