  We give operational meaning to wave-particle duality in terms of
discrimination games. Duality arises as a constraint on the probability of
winning these games. The games are played with the aid of an n-port
interferometer, and involve 3 parties, Alice and Bob, who cooperate, and the
House, who supervises the game. In one game called ways they attempt to
determine the path of a particle in the interferometer. In another, called
phases, they attempt to determine which set of known phases have been applied
to the different paths. The House determines which game is to be played by
flipping a coin. We find a tight wave-particle duality relation that allows us
to relate the probabilities of winning these games, and use it to find an upper
bound on the probability of winning the combined game. This procedure allows us
to describe wave-particle duality in terms of discrimination probabilities.
