(covers information from several alternate timelines)
Coup d'état (pronounced 'kū dā ta') is the sudden overthrow of a government, usually done by a small group that just replaces the top power figures. It is often shortened to simply coup.
The term is French for "a (sudden) blow (or strike) to a state" (literally, coup, hit, and État, state, always written with a capital É in this meaning).
Minister Jaro Essa attempted a coup d'etat on Bajor in 2370. In the wake of the coup, led by Jaro's terrorist front, the Alliance for Global Unity, Jake Sisko and Nog were evacuated from Deep Space 9 on different runabouts. However, although he couldn't pronounce the word quite right, Nog assured Jake that nothing would keep the best friends apart. (DS9: "The Circle")
- Nog: "If our fathers couldn't break us up, no stupid coupe day... coupe day..."
- Jake: "Coup d'etat. It's French."
- Nog: "Well, no stupid French thing will either."
In 2371, Kira Nerys told acting First Minister Kai Winn Adami that Shakaar Edon was not committing a coup by entering the next election for First Minister with the Bajoran Militia's support. (DS9: "Shakaar")
That same year, the Krajensky Changeling told Benjamin Sisko that the Tzenkethi autarch had been overthrown in a coup d'etat, although this was later proven to be a Dominion ruse to start another war between the Federation and the Tzenkethi. (DS9: "The Adversary")
In 2372, General Martok informed Captain Sisko and Lieutenant Commander Worf that the Klingon High Council supposed the recent coup on Cardassia, which had overthrown the Central Command, to have been engineered by the Dominion. Major Kira Nerys later mentioned that a coup on Cardassia was also possible without a Changeling influence since the demise of the Obsidian Order. (DS9: "The Way of the Warrior")
Also in 2372, Admiral Leyton attempted a coup d'état of the Federation starting on Earth, motivated by the Dominion threat. His plans involved reassigning loyal officers to key positions, simulating the passage of cloaked ships through the Bajoran wormhole, and arranging for Red Squad to sabotage Earth's Global power grid. However, Captain Sisko and Odo foiled his plans. (DS9: "Homefront", "Paradise Lost")