Eddie knew that he was not a power player of TT and never would be. He was a devoted hired hand, much like the feudal serfs of medieval Europe. He knew he didn't have Dagny's mind nor Jim's bloodline, and thus would never be part of the TT aristocracy. He was the average guy, the ordinary man -- but a good, loyal, and hard worker.
That is what makes him the feudal serf of TT.