Finesse
The finesse is a playing technique which seeks to make a trick that wouldn't otherwise have succeeded, assuming favourable positioning of a particular card (or two) between the opponents.
For example, consider the following holdings in a given suit, with North to lead:
| North | East | South | West |
|---|---|---|---|
| 2 5 7 9 | 4 10 K | 8 Q A | 3 6 J |
Whatever North leads in this suit constitutes a finesse: if East plays the King, South wins with the Ace, but if East ducks, South wins with the promoted Queen.
For a full treatment, see the wikipedia article on finesses.