(covers information from several alternate timelines)
Toasts were gestures of respect that honored someone or something. They often involved an honorific speech and a shared alcoholic drink. The term referred to the words spoken to commemorate the event, or the drink itself.
The Human act of toasting consisted of three parts: the honorific speech, the agreement, and the symbolic drink. In the speech, one person gave cause for the toast. Everyone else present signified approval by lifting their drinks into the air, often accompanied by verbal assent. Such agreement was offered either with a language-specific, generic toast word (in English, "Cheers!"), or hearty agreement of the honorific speech, with terms such as "Hear! Hear!". Following this ritualistic agreement, the glasses of the participants were usually touched against those of everyone else within reach. The symbolic drink was then taken. If the drink on offer was of a small quantity, such as a shot, the contents were wholly consumed in a single gulp. If not, a generous portion of the total drink was taken, to indicate strong agreement.
On some occasions, a toast was refused. Generally, refusing a toast was a rude act that insulted not just the object of the toast, but the speaker offering the toast. However, if refusal was accompanied by an appropriate explanation, it was possible to disagree with the object of the toast without offending the host. Refusal of the toast was accompanied by the act of pouring out the ritual beverage, or by not holding the offered drink.
There were some Human events that required toasts pro forma, typically legally-significant events such as weddings, military promotions, and the conclusion of commercial or diplomatic negotiations.
Toasts were a rather common celebratory custom, of which there were several notable examples:
- In 2063, Earth warp technology pioneer Zefram Cochrane toasted with members of the USS Enterprise-E who had traveled back in time from 2373 in order to stop a Borg scheme. (Star Trek: First Contact)
- In 2152, T'Pol, Captain Archer, and Commander Tucker toasted to T'Pol having served one year to the day on the Enterprise, longer than any Vulcan had ever served on a Human ship. (ENT: "Carbon Creek")
- Later that same year, Shran offered a toast to "our mutual dissatisfaction" with Soval, Muroc, T'Pol, and Archer, after Archer describes successful negotiations as ones in which neither side is happy. Soval notes that the occasion "merits an exception" to the normal Vulcan dietary exclusion of alcohol. (ENT: "Cease Fire")
- In 2153, Commander Tucker and Captain Archer toasted the memory of Henry Archer as they pondered how his warp engine might help save humanity from the Xindi threat. (ENT: "The Expanse")
- In 2285, James T. Kirk gave a toast in Spock's honor after his death. (Star Trek III: The Search for Spock)
- In 2293, Klingon Chancellor Gorkon gave a toast to "the undiscovered country... the future", ahead of the impending peace talks between the Klingons and the Federation. In return, Leonard McCoy gave a toast to the Chancellor, calling him "one of the architects of the future". (Star Trek VI: The Undiscovered Country)
- In 2364, when Lieutenant commander Data first met his "brother," Lore, Lore introduced him to this Human custom and, using champagne, made a few toasts, one to their discovery of each other, one to Doctor Noonien Soong and one to the Crystalline Entity. (TNG: "Datalore")
- In 2366, Doctor Nel Apgar may have offered the toast "To success" regarding his work on developing Krieger waves as a source of energy, though it was unclear if this actually happened, as the toast was shown in a holographic recreation of events. (TNG: "A Matter of Perspective")
- That same year, when Captain Picard was temporarily replaced by an alien impostor, the impostor visited Ten Forward, ordered ales for everyone there, and then made the toast "Here's to the finest crew in Starfleet." He then stated that when he was in Starfleet Academy, it was traditional to follow every toast with a song and led the crew in singing "Heart of Oak." (TNG: "Allegiance")
- Also that same year, Lieutenant Reginald Barclay ran a holographic program in which he displayed insubordinate behavior towards holographic versions of Lieutenant commander Geordi La Forge and Commander William T. Riker. When the holographic Riker called him out for this, he offered the toast "Here's to insubordination." (TNG: "Hollow Pursuits")
- In 2367, Captain Picard poured two glasses of Chateau Picard and offered a toast to Chancellor Durken after initiating First Contact with the Malcorians. (TNG: "First Contact")
- In 2373, after the USS Voyager returned from an adventure in 1996, Captain Kathryn Janeway summoned the ship's crew to the mess hall and offered the toast "Cheers! To the future!" (VOY: "Future's End, Part II")
- That same year, Jor Brel made a toast to Captain Janeway and her crew for bringing him and his fellow Enarans home. (VOY: "Remember")
- Also that same year, Q brought champagne to Janeway's quarters in an attempt to woo her and offered the toast "To us." Janeway, however, replied that there was no "us." (VOY: "The Q and the Grey")
- In 2375, the Species 8472 Boothby replicant toasted Earth with a two-hundred-year old single malt whisky after capturing Commander Chakotay. (VOY: "In the Flesh")
- Later in 2375, Kai Winn Adami toasted Dukat (who was posing as Anjohl Tennan) with a poisoned drink as a sacrifice for the Pah-wraiths. (DS9: "What You Leave Behind")
- Later that same year, Sisko and Admiral Ross refused a toast of blood wine with Martok on the surface of Cardassia Prime. They noted that, despite their great victory in the Dominion War, so much Cardassian loss of life gave them no cause for celebration. (DS9: "What You Leave Behind")
- In 2376, with the success of the Pathfinder Project, as Reginald Barclay succeeded in establishing contact with Voyager, the Voyager crew made a toast for to Barclay, celebrating his feat, while Barclay and Deanna Troi made a private toast in Barclay's apartment back on Earth. (VOY: "Pathfinder")
- In 2378, the senior staff of the USS Voyager toasted to their long journey and accomplishments through the Delta Quadrant after the future Admiral Kathryn Janeway had arrived on board. (VOY: "Endgame")
- In 2379, the senior staff of the USS Enterprise-E toasted Data, who had sacrificed himself in order to save the ship. "To absent friends" is the same toast Kirk gave in Spock's memory nearly one hundred years prior. (Star Trek Nemesis)
- In an alternate timeline, Harry Kim, as the best man at the wedding of Tom Paris and Kes, attempted to give the toast, but was so nervous that he spilled champagne all over Paris's dress uniform. (VOY: "Before and After")