A "cup of coffee" is a North American sports idiom for a short time spent by a minor league player at the major league level. The idea behind the term is that the player was only in the big leagues long enough to have a cup of coffee before being returned to the minors. The term originated in baseball and is extensively used in ice hockey, both of whose professional leagues (MLB and the NHL) utilize extensive farm systems; it is rarely used in basketball or American football since neither the NBA nor NFL have implemented a true farm system.
One example of how this term is used in a sentence was during the 1996 film The Fan, in which Robert De Niro's character, a middle-aged former pitcher, says, "I was in the bigs for a cup of coffee myself until my arm went south."