Tongo was a strategic Ferengi game that was a combination of cards and roulette and which was played with two to eight players. The object of the game was to win by acquiring as much wealth as possible.
On a given turn, a player could "confront", "evade", "acquire", or "retreat". Each venture had a "risk" amount, a "buy" amount, and a "sell" amount, where the risk amount was equal to the sell amount minus the buy amount. Other possible actions a player could take include "indexing the margin", "indexing the exchange", "leveraging the buy-in", and "converting reserves". (DS9: "Change of Heart")
According to Jadzia Dax, the key to tongo was "to confront when you're sure you're in a better position than the other players. And if your cards match the roll of the dice, you win." (DS9: "Meridian") According to Quark, tongo was more than just "number-crunching"; they had yet to create a computer that could master the intricacies of the game. (DS9: "Change of Heart")
A Global Tongo Championship was held each year on Ferenginar. As of 2373, Zek had won the tournament for twenty-seven years in a row. He also played it for fun. (DS9: "Ferengi Love Songs", "Profit and Lace")
Quark was on a 208-game winning streak over a month-long period during mid-2374 when he beat Jadzia for his 207th victory, causing Worf to lose a bet with O'Brien for a bottle of scotch whisky. O'Brien enlisted Julian Bashir to help beat Quark and end his streak, but Bashir failed when Quark distracted him with talk of Jadzia and Worf's recent marriage to chalk up his 208th victory. (DS9: "Change of Heart")
In early 2375, Quark suggested that letting Worf beat him in a game of tongo would be a great battle and would enable Jadzia to enter Sto-vo-kor. O'Brien told him it would only be enough if he had to "carve his way through a hundred Jem'Hadar to reach the table." (DS9: "Image in the Sand")
The script for "Rules of Acquisition" states that tongo can be best described as a cross between poker, mah-jongg, and craps. There were never any "official" rules established; in an interview on StarTrek.com, Armin Shimerman mentioned that the lack of rules caused continuity problems in terms of which cards were important and how many were dealt. wbm
In Spanish, the word "tongo" is used to refer to cheating in a sporting competition; to "throwing the game". In slang used in Argentina and Uruguay, the meaning is extended to many kinds of scams, lies, or trickeries.