Short for Moralistic Therapeutic Deism. Many people who self-identify as Christians are, in reality, MTD-ists. Core beliefs include (but are not limited to): Sin doesn't exist; You are perfect just the way you are; heaven is a state of mind; God just wants us to be good people; Jesus was a great moral teacher -- but that's it; Don't spread the Gospel.
This can be summarized with the acronym MUSHY:
Make sure not to believe anything that might be embarrassing
Under no circumstance should you defy the culture
Stay soft and pliable in all things at all times
Herald your moral superiority for everyone to see
Y believe the Bible tho lol
Don't be a MUSHY MTD.
A political/worldview term, used to describe anyone roughly left-of-center. Occasionally misspelled and/or misconstrued as "leftleaners" -- a left-leaner (hyphenated) is a moderate leftist; lefterners are not necessarily left-leaners.
All Democrats are lefterners.