Originally Posted by KnockKnock

You left this out of your wiki quote.
A legacy carrier, in the United States, is an airline that had established interstate routes before the beginning of the route liberalization permitted by the Airline Deregulation Act of 1978 and so was directly affected by that Act. Legacy carriers are distinct from low-cost carriers, which, in the United States, are generally new airlines and were started to compete in the newly deregulated industry.[1]

That's the definition. That's it. That's all it means. Why do pilots get hung up on this as if it carries any weight? AA is a Legacy and their product and contract are a regular complaint of my AA buddies. Does that make them less Legacy? Nope, because they've been in business since before 1978!