"Am I not smart enough for this? Is this some kind of experimental avante-garde thing that's just going way over my head? Because unless someone makes an argument, I'm just going to assume that I'm not dumb enough for this; that I've just got too much going on in my head; that I can't absorb something this awful!"
When applied for fiction, the term Lowest Common Denominator means an execution that is designed to appeal to as many people at once as possible.
There are varying interpretations on what this implies. In an egalitarian interpretation, it might be an admirable potential of art; generalized stories that most people can relate to. Stories that all human beings, or at least members of the targeted Demographics, can understand in relation to their own lives. Many tropes came into fiction as fully-formed repeating patterns from real life, colored through a dramatic lens. Also, if we think of media as communication between the creator and the audience, the most successful communication would be the one that is understood by the most people.
From a more elitist point of view, if we assume that a significant percentage of Viewers are Morons, it can be used to mean a work that is made to appeal only to them, instead of more worthy audiences. A show that is marketed to "Joe Sixpack" and all his family, out there in what the suits in New York and L.A. usually call Flyover Country. For maximum profitability, take out everything from the show that anyone more educated, or more devoted to the show, might appreciate, and reduce it to its most shallow parts that even they will understand.
The name of this trope comes from basic fractional mathematics. If we metaphorically imagine individual numbers as the minds of the audience members, some larger and some smaller, the Lowest Common Denominator is the show itself, a number that is calculated by taking all of them into account. If you would think too hard about the metaphor, it would be heavily in favor of the egalitarian interpretation: after all, in mathematics, the LCD itself, the product of a multiplication, tends to be a large number, almost like in The Sons and the Spears metaphor, the result of including everyone is more than the sum of its parts.
Its other common interpretation was probably intended to evoke the 'Greatest Common Factor' concept, a number that is trimmed until it's small enough that it can be used to divide any of the other chosen numbers with it, just like mainstream works are trimmed for Joe Sixpack, but ironically, its users just demonstrated the shallowness that they intended to reference with it, by quickly assuming that any calculation with the words "common" and "low" in it must have a "weak" result.
This could also apply to how the current crop of "hardcore gamers" look upon casual games.
Not to be confused with The Lowest Cosmic Denominator. Or Liquid Crystal Display, for that matter.
No Real Life Examples, Please. Saying that a work was intended for the "Lowest Common Denominator" is highly subjective and hard to define as such. Even a work that was "simplified" was perhaps made as such simply because the author thought it would be a better approach instead. Not to mention, calling a work "made for uneducated people" tends to invite Complaining and heated debates, and we're not really too keen on having that here.