In the money is a term used to describe finishing in a tournament in a high enough position to have won a cash prize.
Sometimes, the term is used to describe players who have won a cash prize larger than their original buyin to the tournament; other times it simply means winning any cash prize at all. Since nearly all tournaments award only prizes that are larger than the buyin, this distinction is normally meaningless.
The verb cash is also used to mean this type of finish: to cash in a tournament is to finish in the money in that tournament. The noun form of cash is sometimes used to mean a finish in the money (as in, "I have three cashes in my last ten tournaments!")
Cashes are usually considered a good start for tournament players and are significant enough that many players count and track them as a meaningful statistic for their own tournament play.