I have reputable sources that used the term "flankerback". From a contract renewal for a "flankerback" for the Chicago Bears in 1965 to a description from a football commentator concerning the best "flankerback" of all time.
A flanker almost always lines up in the slot. Sometimes he might be on the end, but off the line of scrimmage. He does not line up in the backfield. A halfback always lines up in the backfield, although sometimes he might be on the end next to the tight end as an additional blocker. A flankerback can line up in the slot, or in the backfield, and yes Christain McCaffrery is a "flankerback", period.
Again, the "flankerback" was a common term used in the antiquated single wing offense. But has teams continue to utilize halfbacks in the slot, "flankerback" will be making a comeback. It appears Biden is ahead of the curve here. And you people continue to reveal your ignorance. I mean very early on in this thread two other posters posted the definition of a "flankerback". If it didn't exist, there would be no definition. You are a fool, and a disgrace to all the Irish. You are the one that needs to sit down and STFU.