The Chin'toka system was a Cardassian system located near the Federation border. This system contained four planets, two of them inhabited. It was the scene of two major confrontations in the Dominion War. This system was located in the Alpha Quadrant.
At the end of 2374, the system was protected by only five squadrons of Jem'Hadar attack ships because the rest had been diverted to reinforce Dominion forces along the Romulan front. This vulnerability provided an opportunity for Allied forces to launch an invasion of Cardassian space. However, the Cardassians had anticipated their attack and deployed hundreds of orbital weapon platforms in the system. These platforms nearly turned the battle against the Allied forces, until a way was found to neutralize them. Subsequently, the system fell to Allied forces. (see First Battle of Chin'toka) (DS9: "Tears of the Prophets")
However, the invasion did not proceed further than Chin'toka as was hoped; the victorious Allies remained bottled up in the system, fending off constant Dominion attacks. (DS9: "Image in the Sand", "The Siege of AR-558")
The Chin'toka system remained under Allied control for most of 2375, until it was retaken by a combined force of Dominion and Breen warships. An Allied attempt to repel their advance ended disastrously, in which 311 of 312 ships were destroyed with relative ease. This was due to Allied unpreparedness for the Breen energy dampening weapon, which rapidly disabled the fleet, leaving all affected ships completely defenseless (see Second Battle of Chin'toka). The Allies retreated from the system, taking AR-558 with them. (DS9: "The Changing Face of Evil", "When It Rains...")
A close-up shot of a tactical map in the beginning of "When It Rains..." shows the position of the Chin'toka system in relation to Ferenginar, Starbase 375, Cardassia, Bajor and the Badlands. The Chin'toka system was labeled by the AR-558 relay in the map.
A scene cut from "Tears of the Prophets" would have shown that Miles O'Brien came up with the idea to attack Chin'toka, over such alternatives as the Torg'Q system or the Ventani system. The last time he was on a patrol on that part of the border, he had noticed the warp signatures of the ships there to have been changed, suggesting the signatures might have been faked. Garak then suggested ships from the system might have been sent to the Romulan front, leaving the system less defended then previously thought.
An infographic depicting the Chin'toka system in DS9: "Tears of the Prophets" reads: "Chin'toka; Cardassia; binary orbit; perihelion 107 km; aphelion 109 km." The perhelion was a body's point of smallest, the aphelion that of greatest distance from its orbital center. It is not known if these parameters are referring to the binary M-class planets seen in the episode, as this would mean, that the described orbital distance varies by a factor of 100. (Earth's mean distance from the sun is ca. 1.5 * 108 km)
According to the Star Trek: Star Charts (p. 36) and the Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the primary of the Chin'toka system was a G-class star.