Mythical. It was an adjective you used to hear and see quite frequently when a national champion in college football was being discussed, but, now that there's a system which produces a game (no matter that the method by which the game participants are chosen seems to change every year,) it's rarely heard or seen.
In 1984, the Brigham Young University Cougars, playing in a second-tier conference, were the only NCAA Division 1-A football team to go undefeated during the regular season and beat a 6 and 5 Michigan team in the Holiday Bowl, to which they were, as champion of their conference, contractually bound. They were voted best in a poll of coaches and in a poll of sportswriters.
In 2006, the Boise State University Broncos were one of two NCAA Division 1-A teams to go undefeated during the regular season. They don't play in one of the six conferences which devised the current and ever-changing system for naming National Champions, but, under this year's rules, they did qualify to play in a bowl game played in 2007—not, of course, against the other undefeated team, but nonetheless a major bowl. A week ago they played and won a game for the ages against the winningest college football program since World War II, the Oklahoma Sooners, in the same stadium where, last night, the other undefeated team looked nothing like itself in a lopsided and embarrassing defeat.
So, hail and farewell to the 2006 Boise State University football Broncos. In mythical times they might have been called National Champion. Today they were called sixth best by a group of leaders of young men and fifth best by a group of recorders of history.
...and so it goes.