During the second half of the 2000 football season, as it began to appear that the Baltimore Ravens might achieve postseason play for the first time in their history, head coach Brian Billick forbade team members to refer to postseason play by its more conventional name, "playoffs", even finng players who used the Forbidden Word.
Whether this was to make them concentrate more on the games left to be played or was a reflection of some superstition on Billick's part is arguable, and probably doesn't matter.
In response, the players adopted "Festivus" as a euphemism for the term "playoffs", doubtlessly inspired by its use on the television show Seinfeld.
When the Ravens eventually won enough of their games to be guaranteed a spot in the "playoffs", that taboo went away.
But this also guarantees that "Festivus" will live on as a term in football parlance, especially in Baltimore, and especially since the Ravens have succeeded in postseason play to reach (and win!) the Festivus Maximus.