"common denominator" refers to a shared trait or quality that multiple things or people have in common. In mathematics, it specifically refers to finding a number that can be divided evenly by the denominators of different fractions. Full definition
That specific artist who drew that is basically the lowest common denominator of all the artists that draw DBZ promo stuff. (ShonenGameZ.com)
Because you are a black man, you are associated with the lowest common denominator of what the evening news has told society about black men: you must be problematic, lazy, or a thug. (sciencemag.org)
Lumping the movies that appeal to the lowest common denominator in with reading preferences is not a good start. (goodereader.com)