(covers information from several alternate timelines)
Andor was an inhabited planet. By the late 24th century, this Federation world was considered to be of comparable strategic importance as Berengaria, Vulcan and even perhaps Earth. (DS9: "In the Cards"). An array of subspace relay stations linked it to Rigel. (TNG: "Conspiracy", okudagram)
In 2293, the location of Andor in the Milky Way Galaxy was labeled in the star chart The Explored Galaxy, which was on display in Captain James T. Kirk's quarters aboard the USS Enterprise-A. (Star Trek VI: The Undiscovered Country, okudagram)
In 2366, in an alternate timeline, during the Federation-Klingon War, the location of Andor was labeled on a tactical situation monitor in the ready room aboard the USS Enterprise-D. (TNG: "Yesterday's Enterprise", okudagram)
Sometime before 2363, Lisa Cusak, as a junior officer, was assigned as an attaché to the Federation embassy on Andor. She met an Andorian civilian who worked at the Andorian Agricultural Ministry. The two ended up dating for six years. (DS9: "The Sound of Her Voice")
In 2373, Kai Winn rhetorically asked Captain Benjamin Sisko if the Federation would be willing to sacrifice Andor, Vulcan, Berengaria, or even Earth to protect Bajor from the Dominion, if necessary. (DS9: "In the Cards")
See also Edit
Background information Edit
"an-DOOR" was the pronunciation for this planet's name from the script pronunciation guide for "In the Cards". 
In Star Trek: Enterprise's season 4 DVD, writers Judith and Garfield Reeves-Stevens have said the establishment of Andor as a gas giant and the Andorian homeworld, Andoria, as a moon orbiting Andor was devised to help explain the contradiction of why both names "Andor" and "Andoria" have been used interchangeably.
A newspaper article (It's Federation Day!) in the Picard family album, created for Star Trek Generations, suggests that a "Sarahd of Andor" was the Andorian representative present at the forming of the Federation in 2161, though the clipping was not seen on screen and is not considered canon.
Reference material Edit
The Star Trek Encyclopedia (4th ed., vol. 1, p. 24) identifies the gas giant as Andor. Both StarTrek.com and the Star Trek Encyclopedia state that "Andor" was a name which was used interchangeably with Andoria for the Andorian homeworld. The former source does not name the gas giant.
According to the Star Fleet Medical Reference Manual and The Worlds of the Federation, Andor was the eighth planet in the Epsilon Indi system. It was called "Fesoan" by its natives. In the Star Fleet Medical Reference Manual and in Star Trek Maps, Andor was referred to as the Andorian homeworld.(citation needed • edit)
According to the RPG sourcebook Planets of the UFP, Andor was the fifth planet orbiting the star Kuy'va.
According to Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), "Andor" was an alternative name for Andoria (as was "Procyon VIIIA") but was also a J-class gas giant, of which Andoria was a moon.
In Worlds of Star Trek: Deep Space Nine, Volume One, Thirishar ch'Thane and Prynn Tenmei note the differences between the names "Andor" and "Andoria". While Tenmei grew up thinking of ch'Thane's homeworld as "Andoria", ch'Thane grew up knowing it as "Andor". Conversely, ch'Thane grew up thinking of Tenmei's homeworld as "Terra", only to discover that Terrans call it "Earth".
In the novel Lost Souls, much of Andor was devastated by the Borg in 2381. The following year, Andor seceded from the Federation in Paths of Disharmony, although it was later readmitted as a result of the events of Star Trek: The Fall.