While these base schemes are still relevant, they're not as prominent as they once were. Just a few years back when the Redskins franchised Brian Orakpo (an OLB in Washington's 3-4 base), he argued and won that he should be designated and paid like a DE because he was rushing the passer a majority of the time. in this context, what does the term "base" mean? Just as the discussion has established, we're referring to personnel groupings, with a slight variation between the two. Both however, are designed to defend the run and pass equally well. But then, that must also be true of the grouping on offense, which is true. But ask yourself, how often are you seeing just a 2 WR set, with a TE & FB, I-formation personnel? Not that often and certainly not a majority of the time. NFL offenses are in some form of multi-WR set 2/3rd of the time. Some teams are running these sets as often as 70% of the time! What impact does that tend to have on the grouping of your defense? They respond with their nickel & dime groupings, often referred to as "sub" packages. The language hasn't kept up with the reality. Sub always meant situational, but today they're in those sets the vast majority of the time.