Money

Form of trade involving the use of certain materials considered by all involved parties to be of certain inherent value.

As of the 23rd century, the Federation abandoned the use of money, favoring a philosopy of self-enhancement for all. (Star Trek IV: The Voyage Home; and Star Trek: First Contact)

Despite this, the Federation retained a currency based economic system, involving the use of compuer-based "credits". (TOS: The Trouble With Tribbles)

By the 24th century, the majority of non-Federation worlds in the Alpha and Beta Quadrants adopted a monetary system backed by gold-pressed latinum. The Federation government eventually adopted an exchange rate between credits and latinum, so as to further encourage free trade between member and non-member worlds.

Editor's note: It is currently unclear what the exchange rate is between credits and latinum.