The term synthetic referred to any object or material that was created or synthesized by artificial means. The use of synthetics was fairly commonplace in the fields of medicine, cybernetics, genetic engineering, and the industrial, as well as food and beverage industries.
During the 22nd century, medical science was capable of replacing a damaged heart with a synthetic organ. (ENT: "Regeneration")
Menos, a former Vulcan operative, was assigned to infiltrate a cell of smugglers, where became quite adept at smuggling synthetic biotoxins that were used to manufacture transgenic weapons. (ENT: "The Seventh")
During the Malurians undercover operation on the Akaali homeworld, it was discovered by Doctor Phlox, in 2151, that they were contaminating the local Akaali ground water supply with tetracyanate 622. Phlox described the substance as "a synthetic compound primarily used as an industrial lubricant, usually under the strictest safety protocols. It's quite toxic." (ENT: "Civilization")
Later that year, while working with the Valakian physician, Esaak, Doctor Phlox took note that they were treating the patients infected with the genetic disease affect the Valakian people with a synthetic antibody. Esaak noted that it was "effective at first, but the disease mutates. Once it moves into the respiratory system there's no way of controlling it. Pulmonary failure usually follows in a few days." Phlox offered priaxate to help ease their symptoms, and offered to show the Valakians how to synthesize it as much as necessary. (ENT: "Dear Doctor")
One of the processes of the android duplicator on Exo III was the creation of synthetic organ for the android body. Once in place, they could be synchronized with the individual's autonomic nervous system, thus duplicating the rhythms of the original body. (TOS: "What Are Little Girls Made Of?")
The USS Enterprise was diverted to Planet Q, in 2266, to confirm the discovery of "an extraordinary new synthetic food" by Doctor Thomas Leighton, which would have potentially ended the threat of famine on the nearby colony Cygnia Minor. Leighton's call was, however, a ruse. (TOS: "The Conscience of the King") Nevertheless, synthetic food was already part of regular meals aboard the Enterprise, including synthetic meat loaf. (TOS: "Charlie X")
After Spock contracted choriocytosis in 2270, Doctor Leonard McCoy was able to give him injections of a synthesized drug which slowed the disease, however, Spock's body built up an immunity to the drug and it lost its effectiveness, rending the synthetic useless. (TAS: "The Pirates of Orion")
During the USS Enterprise's visit to Angel I in 2364, Lieutenant Commander Data first encountered perfume, a substance he described as "an alcohol-based synthetic, artificially reproducing a floral scent." (TNG: "Angel One")
Setal, the alias of Romulan Alidar Jarok, who was consuming a beverage at Ten Forward aboard the Enterprise-D, described it as "synthetic swill". He inquired to Commander Data if the ship's food terminals were capable of producing a Romulan ale, however Data explained that "I am afraid they would require the molecular structure of the beverage in question. And, as you are no doubt aware, our knowledge of your planet is quite limited." (TNG: "The Defector")
The debris of a Zalkonian vessel found in orbit of an unidentified planet in the Zeta Gelis star cluster in 2366, included pieces of refined metals and other synthetic compounds. (TNG: "Transfigurations")
In 2369, while visiting Ten Forward after spending eighty years in a transporter buffer, Captain Montgomery Scott was introduced to synthehol-based scotch. While complaining about it, his comments were interjected by Lieutenant Commander Data, who explained that it was "an alcohol substitute [that] simulates the appearance, taste and smell of alcohol, but the intoxicating affects can be easily dismissed." As Data spoke, Scott took notice that Data was "not quite Human." Data explained that he was not, but was rather, an android; leaving Scott to make the comparison, "synthetic scotch, synthetic commanders." Data was, fortunately, able to further assist Scott, noting that he believed that "Guinan does keep a limited supply of non-syntheholic products" behind the counter. (TNG: "Relics")
Later that year, Doctor Julian Bashir also met Data, someone who he was familiar with, describing him as "the synthetic lifeform," and offered to later discuss Data's insights on biocybernetic research. (TNG: "Birthright, Part I")
During the Cardassian Occupation, the Bajorans developed an aphasia virus that was later activated aboard Deep Space 9 later in 2369. Upon reviewing the virus, Doctor Bashir took note that it was synthetic, on account of "its nucleotide sequence is too perfect. It's clearly not natural." (DS9: "Babel")
To pose as a male, the female Ferengi Pel made a pair of synthetic lobes to so that she could blend into that society. (DS9: "Rules of Acquisition")
The following year, Lieutenant Reginald Barclay caught a mild case of the Urodelan flu. Doctor Beverly Crusher noted that while most Humans had a natural immunity to it, Barclay's relevant DNA T-cell was dormant, meaning he couldn't naturally fight it off. She, therefore, activated the gene with a synthetic T-cell, to help let his body "attack the infection naturally." Unbeknownst to Crusher, her synthetic T-cell inadvertently created an intron virus that invaded the genetic codes and activated latent introns of other members of the crew. Commander Data, however, was able to create a cure, by using the amniotic fluid from Alyssa Ogawa's fetus as a template for a retrovirus, which neutralized the synthetic T-cell, and re-established the crew's original genetic patterns. (TNG: "Genesis")
The bomb used by the Maquis to destroy the Cardassian freighter Bok'Nor had a casing made of mercassium. When Odo asked if mercassium was some kind of explosive, Commander Benjamin Sisko explained that "it's a synthetic composite used in shield generator construction by the Federation. We don't share that technology with anyone." (DS9: "The Maquis, Part I")
During Data's encounter with the Borg Queen in 2372, this desire to become more Human was brought to the forefront. The Queen, disgusted by Data's endeavor, rebutted the Human form, claiming, "we used to be exactly like them. Flawed, weak, organic, but we evolved to include the synthetic." (Star Trek: First Contact)
In an attempt to cure the macrovirus that affected a number of Garan miners, in 2373, The Doctor devised a synthetic antigen, which was modified for that specific virus so that it would inhibit the virus' ability to replicate. During his work, however, he found that he couldn't figure out how to restore the infected cells to their original condition. (VOY: "Macrocosm")
The material used for making Starfleet uniforms during the 2370s, was discovered to consist of synthetic polymers, and bore a molecular structure that indicated that they were made with replication technology. (VOY: "Distant Origin")
During the Hirogen capture of the USS Voyager in 2374, Harry Kim attempted to repair the heavily damaged ship, he explained to one of his captors, when asked what he was doing, that he was "trying to get the replicator system back online. Unless you prefer the emergency rations? Personally, I'm getting tired of synthetic protein. You're supposed to be the finest hunters in the quadrant, why don't you find us something a little more tasty..." (VOY: "The Killing Game") A short time later, Turanj complained of the wine he was drinking on the holodeck to be "synthetic, and undrinkable." (VOY: "The Killing Game, Part II")
In 2375, The Doctor discovered a viral agent, more specifically a synthetic pathogen, within the vinculum of a Borg cube that began as a biological agent but mutated, so to attack the vinculum's programming. It was determined to have been created by Species 6339. (VOY: "Infinite Regress")
Later that year, The Doctor reported to Neelix that his supply of synthetic antigens were getting low, as well as the ship's supply of medicinal plants Neelix had collected over the past several months. (VOY: "Latent Image")
Still later that year, Seven of Nine discovered the presence of silicon-based parasites on the hull of the Varro generational ship they encountered, which fed on duranium alloys. These parasites eventually migrated to Voyager, affected that ship as well. Further analysis by B'Elanna Torres revealed that the parasites had "artificial gene sequences," and were therefore synthetic. (VOY: "The Disease")
And later yet that year, Doctor Bashir explained that "it's very difficult to keep a supply of synthetic organs on hand in a battlefield situation. You never know how many livers you're going to need, or how many hearts." With the help of Odo, the Doctor attempted to solve that problem during the Dominion War, by attempting to find "the Holy Grail of organ replacement" by having the ability "to find a way to inject the patient with undifferentiated tissue so that can become whatever organ is needed." He had hoped that he could "borrow a cup of goo" from Odo, so as to study the Changeling's morphogenic matrix, in effort to find the means required to "synthesize organic tissue that can change form the way your cells do." Though Bashir ultimately did not find what he needed, but he did discover that Odo was patient zero for the morphogenic virus that was killing the Founders. (DS9: "When It Rains...")
When the Delta Flyer became trapped within a graviton ellipse in 2376, Seven of Nine indicated that the shuttlecraft's computer "isolated several synthetic compounds native to Sector 001," which Tuvok later confirmed to be "titanium and polymer composites." They were later determined to have originated from Ares IV, a 21st century spacecraft from Earth. (VOY: "One Small Step")
During Reginald Barclay's attempt to work with The Doctor to create inoculations based on radiogenic vaccines, The Doctor argued that he didn't believe that they would protect the crew. When Barclay suggested incorporating a predetermined synthetic antigen, The Doctor indicated that it only improved the resistance by ten percent. (VOY: "Inside Man")