Jack Mormon

Jack Mormon is a pejorative term used to describe a baptized member of The Church of Jesus Christ of Latter-day Saints that rarely or never practices the religion. Most "Jack Mormons" support the goals of the LDS Church. They are the LDS equivalent of a "Christmas and Easter Christian" or a "Yom Kippur Jew".

However, in the 19th century, 'Jack Mormon' was also used to describe somebody who was not officially a member of the LDS Church, but who was friendly to Mormons, sympathized with them, and/or took an active interest in their belief system. It is unclear how or why the meaning of the term changed to its current usage, which is almost the reverse of its original meaning.

The term "Jack Mormon" was used by author Edward Abbey in his novel The Monkey Wrench Gang to descibe a character, Seldom Seen Smith, who was a Mormon and had many wives, but was not active in the church or its belief system.