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1.
When two division rival NFL teams meet each other a third time in a playoff matchup after playing each other twice during the regular season.

Can also be used as a synonym for rubber match or tiebreaker in a best-of-three series
The Ravens and Steelers, who each won a game during their home-and-away matchups earlier in the season, will square off in their threematch on Saturday in Pittsburgh. The winner of the threematch advances to the conference final, and the loser goes home.
by Slamnaniganz! January 10, 2011