A casino is a location where various forms of gambling takes place. Modern-day casinos are usually monitored by people to make sure that people under the legal age as well as cheaters (such as "card counters" in blackjack) are not present within the establishment.
In the Smurfs comic book story "The Gambler Smurfs", the Smurfs had an underground casino put into the basement of a random Smurf house so as to hide their gambling activities from Papa Smurf, although he eventually found out and drove out all the Smurfs from there. Also in the same story, the Comte d'Aubenas was planning to turn the entire Smurf Forest into his own private casino, which the Smurfs found out about and prevented from happening with the help of Gargamel.