Even nachos themselves are a relatively new concept. 

Nachos are a fairly modern concept in America. According to a 2002 story in the San Antonio Express-News, they were invented by a man named Ignacio "Nacho" Anaya (thus the name) in 1943 in Mexico. The cheese he used: “Wisconsin cheese, the round one,” the story goes. It was melted on the tortillas and topped with jalapeños. So the original nacho cheese, by this account, was cheddar. 

Then in the 1970s, San Antonio-based Ricos Products marketed a liquid cheddar cheese sauce for nacho chips, which became a concession-stand favorite and is is still available in a can.

But this is where the cheddar consensus ends.

The U.S. Food and Drug Administration defines more than 70 cheeses for labeling purposes but has no definition of nacho cheese. Cheddar cheese, for example, has to have a minimum milkfat content of 50 percent by weight and a maximum moisture content of 39 percent, while blue cheese has to be at least 60 days old. Even brick cheese is recognized as a cheese. Since the agency has no definition of nacho cheese, it can technically be any cheese that isn’t already another kind of cheese. Or something. 

Wait. So, nacho cheese is just whatever we believe it is?