A person who claims to be a 'member' of the Church of Jesus Christ of Latter-Day Saints, but is mostly inactive. Observes some basic principles of 'mormonism', but generally has torn up the rule book. Usually to be found in Utah, where a high concentration of this sect can be found.
A Jack-Mormon often does not observe their guidance of not consuming alcohol or coffee. Can be found to attend the church for say a wedding or funeral. A Jack-Mormon usually, finds themselves at odds with the church. Often this person has been raised in a mormon family unit but come to the conclusion that it does not suit their beliefs.
From experience in Salt Lake City (HQ of Mormonism), this person(typical Jack-Mormon) cannot wait to escape the confines of Utah over the border to Nevada, often going to the small city of Wendover being the nearest to get to, to partake in prostitution, alcohol and gambling.