Your favorite Italian recipe calls for Parmigiano-Reggiano and your best friend's, which is very similar to yours, calls for parmesan. So what's the difference? Or are they the same thing? Well the answer is yes, and no.
You see, Parmigiano-Reggiano, is the only "true" parmesan cheese. This is because it's named after, and produced in, the Parma region of Italy. Parmigiano is simply the Italian adjective for Parma, and parmesan is the French adjective, which we use in America.
However the term parmesan has now become so broad that it now covers cheeses that are similar to (or imitating) Parmigiano-Reggiano. American parmesan is similar in flavor and texture, but has a higher salt content and is aged only 10 months (Parmigiano-Reggiano is aged a minimum of 12 months).
So how do you know if you're getting the real deal? Parmigiano-Reggiano is the only one that will have the words Parmigiano-Reggiano on the rind. No other parmesan cheese will have those exact words.