Unfortunately, there isn't going to be a common definition of "common" for the same reason that there's no common definition of "aesthetically pleasing".
However, as oxymoronic as it sounds, there are common rare coins. With almost 300 different DDR
's documented for the 2000-2008 Lincoln Cents they appear to qualify as "common" varieties by most numismatic standards.
Still cool to find and collect, though.