Q. 1. What is the definition of "layperson?" Is it the same as "Christian?"
A. 1. What is a "layperson?" Laity (laypeople) means the body of the faithful, outside of the ranks of the clergy.
In the Catholic Church, a layperson is defined as anyone who is a Catholic and who is not a priest, a bishop, etc.. (a member of the clergy).
A layperson may or may not be a Christian, depending if he/she has been baptised. A layperson may not necessary be a Catholic.
The laity (laypeople) exists in the Church and outside of the Church.