Gambling was a game of chance and form of recreation that involved betting with currency such as tokens (or chips), money, or latinum, on the outcome of betting games or betting pools. Casinos were popular venues for gambling.
In 2371, Doctor Bashir ordered Major Kira to relax during a particularly stressful period. With the assistance of Quark, Bashir prescribed several means of relaxation, which included a small stack of gambling tokens to use for gambling. (DS9: "Defiant")
Someone who was often quite skilled at a game but hid their true abilities were often called "hustlers". Notable hustlers included Jake Sisko at dom-jot and Kathryn Janeway at pool. (DS9: "The Abandoned"; VOY: "The Cloud")
Interstellar legal status
The Bajoran Provisional Government legalized gambling within Bajoran territory, which included Deep Space 9 and its bar Quark's. Nonetheless, Bajoran law had restrictions against cruelty to animals, and thus Quark's repeated attempts to stage gambling on live Vole fights were still considered illegal on DS9. (DS9: "Through the Looking Glass", "Destiny")
When, aboard the USS Voyager, Lieutenant Tom Paris created the short-lived Paris Radiogenic Sweepstakes, a lottery whose winner was the one to correctly guess the radiogenic particle count the next day, Commander Chakotay shut it down. (VOY: "Meld")
Gambling was legal in the Cardassian Union, as Quark was operating casino games in his bar during the Cardassian Occupation of Bajor. Gambling was also shown to be legal in the Ferengi Alliance and regulated by the Ferengi Gaming Commission. The Ferengi also operated casino ships.