Blatantly stolen from the internets.

What is MOS? Those of you with some Hollywood writing experience will know. In the 50s and 60s the network executives required every TV show (especially sit-coms) to have written into the script what was called the "Moment of Sentiment"... where Ward tells Beaver how honesty is the best policy or
Kitten learns that even if punished, Father Knows Best. Many (jaded) TV writers (among themselves) referred to the MOS segment of their script as the "moment of shit."

Famous by Association
Sitcom writers have a trade term called the "M.O.S."--or "moment of shit." It's shorthand for the formulaic necessity of concluding every show with the sappy, group-hug, ham-fisted moral of the story that's supposed to balance all the misanthropy and cheap one-liners that came before it.

The show itself was a half hour situation comedy pilot entitled My Ex-Life produced by Richard Appel, directed by Kelsey Grammer and starring Tom Cavanagh (Ed) and Cynthia Watros. The plot was predictable. A divorced couple tries to prove how well adjusted they are. A deception is created and then foiled forcing the couple to confront their feelings in a MOS, a Hollywood acronym for "Moment of Shit," that brief part of the comedy, usually in the second to last scene in which the characters get serious, bare their souls and achieve some level of closure. This pilot actually had two MOSes, a dramatic double-whammy. The writing was tired, the 4,902nd rehashing of familiar material by familiar characters in an all too familiar setting.