A chair was a piece of furniture which was designed for a humanoid figure to rest upon and therefore relieve pressure of the legs and back. Chairs were of such practical design that this furniture piece evolved in nearly every known humanoid culture across the entire Milky Way Galaxy.
Chairs came in a wide variety of size and design. In the 19th century on Earth, upper-class citizens typically had elegant looking plush chairs about their residences. (TNG: "Ship in a Bottle") The term "chair" may also refer to the head of an organization or a position of prestige. The Lucasian Chair is considered a position of some importance at Earth's Cambridge University. (TNG: "All Good Things...")
The prevalence of chairs in most every humanoid culture could perhaps be attributed, in some portion, to Hodgkin's Law of Parallel Planetary Development. On 892-IV, a society identical to 20th century Earth had developed (albeit where the Roman Empire never fell) with this parallel world including such common Earth furniture items as lamps, chairs, and tables. (TOS: "Bread and Circuses")
On board most starships, chairs were common for the crews to sit in and perform their duties over long hours of watch. At the center of every starship, there was often a command chair, for the commanding officer of the ship to direct shipboard operations. Command chairs of this nature were seen on starship types of nearly every spacefaring species to include the Klingons, Romulans, Cardassians, Ferengi, Tamarians, and the starships of the Federation Starfleet.
The Borg were an exception to this, since Borg cubes had no recognizable bridge or command center and Borg drones used alcoves to regenerate. Chairs were therefore impractical for the Borg. (TNG: "Q Who") The Dominion did not use chairs on board their starships, something a Human crew noticed almost immediately when operating a stolen Jem'Hadar fighter. (DS9: "A Time to Stand")
Lieutenant Worf kept a futuristic looking chair in his quarters aboard the Enterprise-D. (TNG: "Peak Performance", "Family", "Reunion", "Redemption", "New Ground", "Cost of Living", "A Fistful of Datas", "Birthright, Part I", "Parallels", "Genesis", "Firstborn")
In at least one case, a chair was used in a scientific experiment. In 2369, Commander Data attempted to use a transporter to beam a chair off of a holodeck. It was later discovered that the experiment itself was flawed since the transporter being used was a holodeck simulation and, as no one had ever attempted to beam a chair off a holodeck, there was no frame of reference for the holodeck simulation to access. (TNG: "Ship in a Bottle")
Chairs also had occasionally been used as instruments of torture.
When Jonathan Archer and Travis Mayweather were being held by the Tandarans, T'Pol and Tucker discussed their legal rights. T'Pol said that the Vulcans could send an arbitrator, but Tucker was so surprised that he thought the electric chair, an early form of punishment on Earth, would be better suited to them. (ENT: "Detained")
In 2154 Soval was directly beamed into an interrogation chair on board the Andorian starship Kumari, where he was tortured, including the use of a neuro-synaptic field which lowered his emotional barrier. Commander Shran noted that the device had numerous successes in luring information out of Vulcan operatives. (ENT: "Kir'Shara")
In 2269, former Fleet Captain Garth, while an inmate at the criminal asylum on Elba II, took over the facility including the therapy equipment used to rehabilitate prisoners. Garth modified a rehabilitation chair, which normally was a painless device designed to relax patients, into a torture device that was "exquisitely painful". Both James T. Kirk and Donald Cory were forced to sit in the torture chair while Garth tormented them. (TOS: "Whom Gods Destroy")
Doctor Tristan Adams also was known for turning medical therapy equipment into torture devices. In 2266, Doctor Adams developed the neural neutralizer which was a device designed to empty a person's mind of harmful thoughts while they sat in a chair in a special room. Doctor Adams modified the neutralizer to not only empty a person's mind but fill it with other thoughts of his own design. Simon Van Gelder was an early victim of the neural neutralizer with Captain James Kirk also tortured in the neutralizer chair by Doctor Adams. (TOS: "Dagger of the Mind")
The Romulans also used chairs as a device for torture. In 2367, Lieutenant Commander Geordi La Forge was taken aboard a Romulan warbird, strapped into a torture chair, and his VISOR implants fed several images of "horrors" in an effort to brainwash him. (TNG: "The Mind's Eye")
See also: Rostrum
Memorable quotes involving chairs
"Mr. Spock, what happened?!?"
"The occipital area of my head seems to have impacted with the arm of the chair."
"The chair is no longer painless. It is in fact, exquisitely painful."
"Just have your Klingon servant bring us some chairs!"
"And you may have...MY chair."
"Captain, is there something wrong with your chair?"
"Get out of my chair!"
"And get these chairs off the bridge."