If Ordinary People were published these days instead of in 1976, it might be called Basic People, because you just know the Jarrett family is the type to order a pumpkin spice latte from Starbucks and complain that the barista misspelled their name on the cup.
Okay, "ordinary" and "basic" have slightly different definitions, so the comparison isn't entirely on point. The Jarrett family just wants to be normal, and today, that's easy to do by jumping on various pop culture fads like PSLs (we're embarrassed "pumpkin spice latte" has an acronym) or jeggings.
In the 1970s, being "ordinary" wasn't as easy as buying a fancy coffee drink. Conrad struggles to be "ordinary" to move past his suicide attempt and live up to his dead brother's legacy. Calvin struggles to be an "ordinary" father by trying to make sure his other kid doesn't die. And Beth struggles to be an "ordinary" mom by ignoring her family and pretending to be perfect.
This strategy works out about as well as if you pretended you had a latte. Guess what? You still wouldn't have a latte.
Conrad eventually learns that everyone has troubles, which means that no one is ordinary. But since everyone has problems, then everyone is ordinary. Our differences and our flaws make us ordinary. What nobody is is perfect—and that includes Beth.
The word "ordinary" appears at two major times in the book. The first is shortly after Conrad quits the swim team: "So truth is in a certain feeling of permanence that presses around the moment. They are ordinary people, after all. For a time they had entered the world of the newspaper statistic; a world where any measure you took to feel better was temporary, at best, but that is over. This is permanent. It must be" (11.85).
At this point, Conrad feels like his family's life has returned to normal after his brother's death and his own suicide attempt. He thinks this state is permanent—but it's actually just a bubble, because all they're doing is ignoring the problems. Eventually the bubble will burst.
The other appearance of the word ordinary is when Conrad is briefly stopped by a police officer during a late night walk: "All the outer signs must be right. […] You're all right kid. Ordinary"(26.62). Here, Conrad realizes that just because he can pass as ordinary, which his mom does, that doesn't mean he's ordinary on the inside. Ordinary is only skin-deep.