A trade route was a network of locations which was regularly used in the commercial transport of cargo.
In the mid-22nd century two Osaarian merchant ships entered the Delphic Expanse to search for new trade routes. (ENT: "Anomaly")
When Enterprise discovered a time travel pod in 2152, it was more than thirty light years from the next trade route. (ENT: "Future Tense")
Alixus chose Orellius as the site of her colony in the 2350s since it was far from any trade route. (DS9: "Paradise")
By 2366, the raids of the Gatherers had disrupted Federation trade routes in the vicinity of Acamar III. (TNG: "The Vengeance Factor")
Galorndon Core was along the Barolian trade route with the Romulan Star Empire in 2368. (TNG: "Unification II")
In 2370, Galador freighters operated on a trade route between Galador II and Farius Prime. (DS9: "The Maquis, Part I")
By 2372, Bopak III was well off established Gamma Quadrant trade routes. (DS9: "Hippocratic Oath")
According to Adin in 2373, a trade route close to Ilari was often plagued by mercenaries and thieves. (VOY: "Warlord")
Since Adin lied about most other things it is unclear if such a trade route actually existed.
In 2376, Gedrin initially claimed the Vaadwaur had used the underspace as trade routes, though they had in fact used it to attack and conquer other planets. (VOY: "Dragon's Teeth")