So, imagine there is a girl named Molly. She is a very good girl who always follows the rules and does everything she is supposed to do. And people call her a "Molly Mormon."
"Mormon" is a word that refers to a religion that some people follow called The Church of Jesus Christ of Latter-day Saints. In this religion, people try to live their lives in a certain way, and being a "Molly Mormon" means that you do everything you are supposed to do according to this religion.
For example, Molly might go to church every Sunday, say her prayers every night, read from a book called the Book of Mormon, and never do things like drink alcohol or swear. She might also be very honest, kind, and helpful to others.
Some people might think that being a "Molly Mormon" is a good thing, while others might not like it because they think it means that Molly is too perfect or too judgmental of others who don't live the same way she does.
But no matter what anyone thinks, it's up to Molly to decide how she wants to live her life and what kind of person she wants to be.