Ten Forward is a lounge and recreation facility located on Deck 10, section 1 of a Galaxy-class starship. (TNG: "Power Play", "Deja Q") Ten Forward has much the same function as a mess hall on smaller starships.
Ten Forward is situated at the extreme forward end of the saucer section and is designed with several large windows, which offer a spectacular view of space ahead of the vessel. The room is accessed by two doors, on the port and starboard sides at the rear of the room. The location serves as the social center of the ship and is equipped with a number of recreational activities such as three-dimensional chess, Terrace, and Strategema, tables and seating, and a bar which serves several alcoholic and syntheholic beverages. Two replicator terminals behind the bar are able to produce other food and drinks. (TNG: "The Child", "Peak Performance", "Ménage à Troi", "Conundrum", "Relics"; ENT: "These Are the Voyages...") There is also dedicated wait staff who serve patrons both at the bar and at the tables. They are generally civilian members of the crew and wear uniforms with a green color palette. (TNG: "Deja Q", TNG: "Lower Decks")
Ten Forward can also be used for many official shipboard functions, such as weddings (TNG: "Data's Day", "Cost of Living"), diplomatic gatherings (TNG: "The Price", "Ménage à Troi", "Liaisons", "Dark Page", "Journey's End"), the change of command ceremony (TNG: "Chain of Command, Part I"), birthday and other parties for individual ship personnel (TNG: "Future Imperfect", "The Measure Of A Man", "Preemptive Strike"), concerts (TNG: "Sarek", "In Theory", "Lessons", "Second Chances", "Inheritance"), poetry readings (TNG: "Schisms"), and funerals. (TNG: "The Next Phase")
On the USS Enterprise-D, the Ten Forward lounge was hosted by the El-Aurian Guinan, who came aboard the ship in 2365. (TNG: "The Child") She was afforded a small office adjacent to Ten Forward as part of her duties. (TNG: "Q Who") Guinan kept a variety of non-syntheholic drinks in Ten Forward, including a bottle of Aldebaran whiskey given to her by Captain Jean-Luc Picard. (TNG: "Relics") There was a large fiber-optic mural displayed on the wall behind the bar aboard the Enterprise; the artwork represented the Milky Way Galaxy seen from an oblique angle.
When Wesley Crusher inadvertently released a breed of sentient nanites aboard the Enterprise in 2366, Ten Forward was one of the locations where he set up traps in an attempt to contain the machines. (TNG: "Evolution")
Lieutenant Commander Data believed that spending time observing Human social interaction in Ten Forward would be beneficial for his android "offspring", called Lal. She worked there for a brief period, under the supervision of Guinan. (TNG: "The Offspring")
When Ambassador Sarek of Vulcan visited the Enterprise in 2366, side effects from Bendii Syndrome began to project negative emotions on the Enterprise crew. Ten Forward became the site of a brawl, injuring several crew members. (TNG: "Sarek") There was more violence in Ten Forward in late 2367, after REM sleep-deprived crew members began to draft conspiracy theories about the Enterprise's inability to escape the Tyken's Rift. Guinan was able to defuse the situation, thanks to a weapon she had acquired on Magus III. (TNG: "Night Terrors")
In 2367, Chief Miles O'Brien wed Keiko Ishikawa in Ten Forward. (TNG: "Data's Day") Ten Forward also became the birthplace of their first child one year later, in 2368. The Enterprise had been struck by a quantum filament, disabling most ship's systems and cutting Ten Forward off from sickbay. Keiko was in Ten Forward at the time, and assisted Lieutenant Worf in treating injured survivors. She subsequently entered labor, and Worf acted as midwife during the delivery. (TNG: "Disaster")
While investigating the disappearance of the USS Essex at Mab-Bu VI in 2368, Counselor Troi, Commander Data, and Chief O'Brien were inhabited by the noncoporeal Ux-Mal criminals. They attacked the bridge crew and then stormed Ten Forward, taking several hostages and injuring several crew members. Attempts by Enterprise crew to force the entities from the officers failed, and the hostages were finally freed when Captain Picard deceived the criminals into believing he would transport the rest of the spirits aboard. (TNG: "Power Play")
Ten Forward was chosen by Ambassador Lwaxana Troi for her wedding to Minister Campio in 2368. Although Captain Picard was initially irritated that the ambassador believed she could use the Enterprise at her disposal, his demeanor changed when he learned he would be acting as father of the bride. The wedding was later canceled when Troi offended the minister's strict protocol requirements by arriving at the wedding in the nude, in traditional Betazoid fashion. (TNG: "Cost of Living")
After it was believed Lieutenant Commander Geordi La Forge and Ensign Ro Laren had been killed in a transporter accident during a rescue mission to a damaged Romulan science vessel in 2368, Commander Data planned a memorial service for the two officers which was held in Ten Forward. The service was non-traditional and was upbeat instead of mournful and solemn, which was met with approval by the Enterprise crew. This would prove to be fortuitous – Ro and La Forge were very much alive, having actually been "phased" due to chroniton exposure from an experimental interphase generator aboard the Romulan ship. They were able to create a sufficiently large chroniton field in Ten Forward, requiring a heavy anyon sweep to eliminate them. The anyon field temporarily rephased Ro and La Forge just enough so Picard and Data could see them, leading Data – realizing that the numerous unexplained chroniton fields popping up throughout the ship had been caused by their presence – to initiate a high-powered anyon sweep, which completely returned the pair to normal phase. (TNG: "The Next Phase")
Ten Forward was the last area of the ship to be decontaminated during the baryon sweep in 2369. Picard and the terrorists attempting to steal trilithium resin from the Enterprise went to Ten Forward to await pickup by a small vessel. Picard narrowly escaped death, as the baryon sweep was discontinued mere meters from the edge of the windows. (TNG: "Starship Mine")
Alternate timelines and realities
In an alternate version of 2366, created when the USS Enterprise-C disappeared from the year 2344, Ten Forward was suitably altered to befit the military nature of the new timeline. Luxuries were limited, the civilian wait staff was gone, and crew members were often forced to consume TKL rations, since replicator power was generally diverted to the defensive systems. (TNG: "Yesterday's Enterprise")
Ten Forward was still aboard the refit USS Enterprise-D of the anti-time future experienced by Captain Jean-Luc Picard. It had been slightly altered, with a new piece of artwork replacing the Milky Way mural. (TNG: "All Good Things...")
Ten Forward was introduced in TNG: "The Child", the first episode of the second season of Star Trek: The Next Generation. However, TNG: "All Good Things..." established that it was an unseen part of the ship until then.
In the TNG Season 2 DVD special feature "Mission Overview: Year Two", Ten Forward was discussed by Rick Berman, Jonathan Frakes, Marina Sirtis, Maurice Hurley, and Peter Lauritson. According to Berman, the production had some space over, following a move of the sets, and they discussed what they could build. They decided to show a place where the crew members could be off duty. On every other set, the crew members were always shown on duty.
The set for Ten Forward was created in the interim between the show's first and second seasons. It was designed by Production Designer Herman Zimmerman, and was the last standing set he supervised for TNG. Zimmerman also considered the Ten Forward set as being the final significant Galaxy-class set that was designed for the series. (Star Trek: The Magazine Volume 2, Issue 12, p. 25) However, the designer of the Enterprise, Andrew Probert, did not intend for that part of the ship to represent lounge space. Rather, he preferred clusters of windows located further up on the saucer section. 
Illustrator Rick Sternbach designed the Milky Way mural in Ten Forward. "I had a lot of fun suggesting various bits of art for Ten Forward," recalled Sternbach. "After showing them a number of abstractions, it came down to an impressionist view of the Milky Way Galaxy. The whole thing was rimmed in light, and the different layers received very heavy-duty fiber optics, which were lit and cycled. It turned out to be a nice piece that complemented the room." (Star Trek: The Magazine Volume 3, Issue 2, p. 98)
Set Decorator John Dwyer enjoyed the task of working on the Ten Forward set, later remarking, "The only thing we didn't do was put all those cooking appliances and stuff in. We didn't have any of that, we had a bar. If you look at it later on, they had a little barbecue set up in there!" (Star Trek: The Magazine Volume 2, Issue 12, p. 25)
Filming on the Ten Forward set while keeping the action quotient constantly high occasionally proved difficult, such as during production on "Power Play", which made extensive use of the set. David Livingston, who directed that episode, explained about the environment, "It's like shooting on an aircraft carrier, it's a big empty room." (Captains' Logs: The Unauthorized Complete Trek Voyages, p. 239)
The doors of Ten Forward were originally seen as part of Starfleet Command in TNG: "Conspiracy". The set was redressed to serve as a concert hall in TNG: "Sarek" and a theater in "The Nth Degree" and "Frame of Mind". It was also heavily redressed to represent the office of the Federation Council President in Star Trek VI: The Undiscovered Country. After filming on Star Trek Generations was completed, the set was refurbished to become the mess hall of the USS Voyager on Star Trek: Voyager. Its windows were flipped upside down and used in the captain's ready room and briefing room.
A corner portion of the set was rebuilt for a brief scene during the first act of ENT: "These Are the Voyages...", integrated via computer with a clip of the rest of the set from the TNG episode "Ménage à Troi".
It has been suggested by Star Trek: The Magazine, among other sources, that the banquet area seen aboard the USS Enterprise-E during the beginning of Star Trek: Insurrection is that ship's Ten Forward. Although the room was on Deck 10, there was no dialog or signage which explicitly identified it as Ten Forward. Also, there is no evidence to suggest that Ten Forward was a feature of every Galaxy-class starship. It may have been unique to the Enterprise-D, although all Galaxy-class ships seen possess the distinctive window arrangement of Ten Forward at the bows of their saucer sections.
One of the door pairs for Ten Forward was sold off in the It's A Wrap! sale and auction.  In the auction, it was stated that the doors are made up of wood, painted brown, while the viewports are smoked acrylic. The doors are operated by two runners on the top of the structure. Several glasses were also sold off on the It's A Wrap! auction.  
"Ten Forward" is also the name of a coffee shop in Los Angeles.
Outside of canon information, some novels and comics have referred to this area on Galaxy-class starships other than the Enterprise-D. The USS Excalibur (NCC-26517-A) has a Deck 10 bar area, but it is referred to as the "Team Room" by the crew in the Star Trek: New Frontier stories of Peter David. The USS Challenger's Ten Forward has been replaced with a "Shuttlebay Four" according to The Return, a novel by William Shatner (with Judith and Garfield Reeves-Stevens).