(covers information from several alternate timelines)
A conference room was a location where meetings and similar gatherings were held.
The NX-class Enterprise had a conference room. (ENT: "Stigma", "E²", et al.) The room was oftentimes used to host interspecies negotiations, as part of Enterprise's role in shaping alliances. Conferences between Andorians, Tellarites, and Vulcans were held here. (ENT: "Stigma", "Babel One", "United", "The Aenar", et al.) The room was equipped with a conference table, several seats, and a companel. (ENT: "Stigma", "The Expanse", et al.)
While the Interspecies Medical Exchange was hosting a conference at a facility on the surface of Dekendi III in 2152, an area of the building which was reserved for a Vulcan contingent included a Vulcan conference room. At one point during the IME conference, this room was used for a hearing attended by not only Vulcan doctors Strom, Oratt, and Yuris but also Enterprise captain Jonathan Archer and Vulcan Sub-Commander T'Pol. The hearing mainly regarded Pa'nar Syndrome and T'Pol having recently been recalled to Vulcan due to concerns over the fact she had contracted the syndrome. However, Dr. Yuris also took the opportunity to concede several revelations, including that he also had Pa'nar Syndrome and that T'Pol was not responsible for having initiated a Vulcan mind meld that had led her to acquire the affliction. (ENT: "Stigma")
Later that year, Captain Archer and Commander Charles Tucker III waited in Enterprise's conference room prior to the arrival of Vulcan Ambassador Soval and Sub-Commander Muroc. After the pair of Vulcan visitors were escorted into the room by T'Pol, a short meeting was held by all five there, prior to Archer and T'Pol visiting the planet Weytahn. Once they returned, they as well as Soval and Muroc met again in the conference room, having arranged to escort Soval into peace talks with the Andorians on Weytahn. After he together with T'Pol and Archer managed to meet with Andorian Commander Shran, all four, along with Muroc, attended another meeting in the conference room, Shran suggesting a toast to mark the start of the peace talks. (ENT: "Cease Fire")
In 2153, Enterprise's conference room was used for a meeting between Captain Archer and a trio of Vissians – specifically, Captain Drennik, a chief engineer, and his wife, Calla. They considered a recent appeal to Enterprise for asylum, a request which had been submitted by the cogenitor Charles. (ENT: "Cogenitor")
Later that year, a briefing was held in Enterprise's conference room. Sub-Commander T'Pol, Lieutenant Malcolm Reed, Ensigns Travis Mayweather and Hoshi Sato, as well as Doctor Phlox were in the room when Commander Tucker arrived. They chatted about the upcoming briefing but stopped when Captain Archer entered the room, with news that a probe had recently committed an attack on Earth. Also, Archer was told, via the room's companel, that the ship was receiving a transmission from Admiral Forrest. Lastly, the captain ordered Ensign Mayweather, the vessel's helmsman, to set a course for Earth at warp five. (ENT: "The Expanse")
On Lorian's recommendation in 2154, he and Karyn Archer had a discussion with Captain Archer and T'Pol in the conference room aboard Enterprise shortly after the two groups met each other for the first time. (ENT: "E²")
Later in 2154, the conference room on Enterprise was used for a meeting between Archer, T'Pol, Vulcan High Command Administrator V'Las, Vulcan Security Directorate Chief Investigator Stel, and Ambassador Soval. The discussion revolved around identifying suspects of the recent bombing of the United Earth Embassy, with the Andorians and Syrrannites named as the potential culprits. Eventually, the Vulcans granted Archer permission to inspect the remains of the embassy himself.
Shortly thereafter, Enterprise's conference room was used for a meeting between Commander Tucker, Phlox, Soval, Stel, and V'Las. They discussed evidence that Stel was guilty of the embassy bombing and talked about the fact that the "evidence" had been obtained by Soval via a Vulcan mind meld, although that technique was generally considered highly distasteful by Vulcan society. (ENT: "The Forge")
Soon afterwards, the conference room was used by Commander Tucker, Soval, and Shran. Soval warned Shran about an imminent invasion of Andoria that the Vulcan High Command was planning. Shran was extremely skeptical of this news but eventually decided to discuss the claim with his superiors. Tucker advised Shran to be expedient about doing so. (ENT: "Kir'Shara")
In the mirror universe, another conference room was aboard the ISS Enterprise (NX-01). The room, in 2155, was used for a meeting between Captain Maximilian Forrest, Commander Jonathan Archer, T'Pol, Tucker, and Sato. While a star chart was displayed on the room's monitor, Archer demonstrated evidence that the USS Defiant, a 23rd century starship from a parallel universe, had been captured by Tholians and was currently in their territory. Though the others in the room were skeptical, Forrest demanded they investigate the proof, then exited the room. (ENT: "In a Mirror, Darkly")
In 2366, Captain Jean-Luc Picard ordered the senior staff of the USS Enterprise-D to the vessel's conference room to discuss a series of computer malfunctions occurring on the ship. (TNG: "Evolution") The conference room on Galaxy-class starships was located on deck 1, directly behind the main bridge and was more commonly known as an observation lounge. (Star Trek: The Next Generation)
Following their 2374 arrival at Starbase 375 aboard the IKS Rotarran, Captain Benjamin Sisko and his senior staff were asked to beam directly to the starbase's conference room to be debriefed by Admiral William Ross on their successful mission destroying a Dominion ketracel-white facility. (DS9: "Sons and Daughters")