Cloud City is an outpost and a tibanna gas mining colony on Bespin. It is named such because it was perpetually surrounded by giant clouds. It is run by Lando Calrissian in Star Wars: The Empire Strikes Back.
Cloud City is located on Bespin. It owns a Tibanna Gas mining operation. Sometime during Emperor Palpatine's rule, the city came under the leadership of Lando Calrissian. Because Tibanna Gas was highly coveted by the Empire, Lando always feared discovery and takeover by the Empire. Han Solo, Chewbacca, Leia Organa came to Cloud City to have the Millennium Falcon repaired after escaping the Empire following the Battle of Hoth using a feint. Unfortunately, Boba Fett, who saw Obi-Wan Kenobi pull a similar feint on his father, saw the feint for what it was and after the Falcon showed itself was able to deduce whare they were headed and sent his report to Death Squadron, Darth Vader's personal armada. Thanks to having functional hyperdrives, Death Squadron arrived before the Falcon and Vader made a deal with Lando; if he helped them nab Luke Skywalker and his friends, he would leave Cloud City in peace. Lando agreed to the deal and the trap was sprung; Han and his friends were captured by Vader and used as bait to lure Luke into a trap. Luke arrived and faced Vader in a duel and was defeated. All seemed lost for the Rebels until Lando rescued them and helped them escape.