A Jack Mormon is somebody raised in Mormonism who still identifies with the Mormon culture to some extent, but not the belief system or the church. They may attend services on occasion but not regularly, or they may not attend at all and hold agnostic beliefs. Even those who remain in the church do not follow its teachings regarding such things as drinking alcohol and coffee.
 Jack Mormon culture
A Jack Mormon culture consists of Jack Mormons who continue to identify with Mormonism because it is their heritage, but do so on a joke religion basis in the same manner as religions like Discordianism and the Flying Spaghetti Monster. They know all the Mormon in-group slang, history, and customs and use them in ironic and humorous ways.
In places like Salt Lake City, Park City, Price, and Moab, Utah where the population is significantly non-Mormon, Jack Mormonism also tends to thrive, with Jack Mormons and non-Mormons alike going out of their way to flaunt their sinfulness.
 Non practising Mormons
The above is not true of all Jack Mormons however. Many are simply inactive in the church or "backslidden", and drink, smoke, swear, smoke marijuana, masturbate, and fornicate, and go to church maybe once a year on Christmas. During the 1970s and 80s when Mormon voting patterns shifted heavily toward the Republican Party, the "Jack Mormon" accusation was often used for Mormons who voted Democratic.
 Committed Mormons who reject some beliefs
There is a somewhat related phenomenon of dissident reformists and liberals who remain active within the LDS church and continue to believe in its religious beliefs, but seek to change the church's position on gay rights, birth control, abortion, environmentalism, or feminism. Technically not Jack Mormons, they are accused of such anyway, and the LDS church quietly tries to tolerate the quieter ones and frequently disfellowships or excommunicates the more active ones.
 Molly Mormon
A "Molly Mormon" should not be confused with being the female version of the "Jack Mormon", as the "Molly Mormon" is normally very active in her ward and sincere in her beliefs and deep in her indoctrination.