Ferenginar was an inhabited planet in the Alpha Quadrant. This was the homeworld of the Ferengi, a warp-capable humanoid species. It was the capital world of the Ferengi Alliance. Ferenginar was surrounded by star systems, like Clarus and Irtok, that an invading force would have to conquer first.
The planet's capital city was primarily a series of low domes broken by a tall spire, the Tower of Commerce, which stood in the center of the Sacred Marketplace, and was the seat of power of the Grand Nagus, the leader of the Ferengi Alliance.
The planet was best known for its nearly constant, planet-wide torrential rains, rotting vegetation, and rivers of muck.
In 2375, the location of Ferenginar was labeled on a tactical cartography map that was displayed in the wardroom of Deep Space 9. Ferenginar was located approximately fifty-five light years from Cardassia Prime and Starbase 375 and sixty light years from Bajor. (DS9: "When It Rains...", okudagram)
In the mid-24th century, Ferenginar experienced rampant inflation and currency devaluation after the Great Monetary Collapse. Many accounts, including some belonging to Quark, were devastated. (DS9: "Homefront")
In 2374, after Grand Nagus Zek added an amendment to the Ferengi Bill of Opportunities allowing females to wear clothes and make profit, Ferenginar was plunged into financial chaos and a communications blackout was imposed. (DS9: "Profit and Lace")
In DS9 Season 3 installment "Family Business", the Ferengi homeworld first received its name. "fer-ENG-ih-nar-" was the pronunciation for this planet's name from the script pronunciation guide for fourth season episode "Bar Association". 
While writing "Family Business", Ira Steven Behr and Robert Hewitt Wolfe had a lot of fun with devising details about Ferenginar, for viewers' initial glimpse of the planet. Thinking about Ferengi anatomy, Wolfe decided the planet should have "a moist climate." The writers also wanted to differentiate Ferenginar from other major homeworlds in Star Trek, which commonly had "hot and dry" environments, related Wolfe. Seeing as rain hadn't been depicted much on alien planets, the writers chose to give Ferenginar a virtually permanent rainy climate. (Star Trek: Deep Space Nine Companion, p. 241)
A scene description from the script for "Family Business" reads, "Ferenginar, the homeworld of the Ferengi, is a fetid dismal swamp, subject to a near-endless downpour. The capital city of the homeworld rises out of the swamp, a series of dome-like structures piled almost haphazardly one atop another." The capital city was also established, in the script, as containing the Sacred Marketplace in the center and the Tower of Commerce within the marketplace. 
Following the debut appearance of Ferenginar in "Family Business", Ira Behr remarked, "It was an interesting look at the Ferengi homeworld [....] I'm not sure we'll be going back to the Ferengi homeworld." (Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages, p. 97)
In ultimately excised dialogue from the first draft script of DS9 Season 4 outing "Body Parts", Garak commented about Ferenginar, "I must admit it's a magnificent city... I quite enjoyed my time there." This would probably imply either that Ferenginar had only one city or that the planet's capital city was at one point intended to have the same name as the planet.
Creating the sets to represent Ferenginar in DS9 Season 5's "Ferengi Love Songs" was fairly easy, with the Grand Nagus' Chamber of Petitioners in the Tower of Commerce being the only new set. Because Ishka's house had been established in "Family Business", DS9's art department had to merely assemble and redress that set, so that it could reappear in "Ferengi Love Songs". (Star Trek: Deep Space Nine Companion, p. 445)
According to the Star Trek: Star Charts (pp. 35 & 36) and the Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the M-class planet Ferenginar was located in the Ferenginar star system. The capital of this world, and of the Ferengi Alliance, was Ferenginar. In 2378, there were 78.2 billion Ferengi living on this world. The Ferengi have been warp-capable since antiquity. Major points of interest were the Sacred Marketplace and Tower of Commerce. The primary of the system was a M-class star.
According to the Star Trek Encyclopedia (3rd ed., p. 152), Ferenginar was a M-class planet.