A squadron was a grouping of starships or aircraft for combat engagements. The term was generally applied to a small grouping of ships that were organized to fight as a unit. The Federation, the Klingon Empire, the Romulan Star Empire, and the Dominion are examples of powers who used squadrons.
In the Xindi military, a squadron was typically comprised of two or three Xindi-Reptilian warships and an equal number of Xindi-Insectoid ships. One example squadron was led by Commander Dolim and guarded Azati Prime while the Xindi superweapon was being constructed there in early 2154. (ENT: "Azati Prime")
The Klingon Defense Force operated squadrons of the Birds-of-Prey. In 2367, Kurn commanded the allegiance of four squadrons just prior to the outbreak of the Klingon Civil War and was able to convince three of them to join on the side of Gowron. (TNG: "Redemption")
In Starfleet during the Dominion War, flights of Federation attack fighters were grouped into squadrons. These ships played important roles in both Operation Return and in the Battle of Cardassia. (DS9: "Sacrifice of Angels", "What You Leave Behind")
The Jem'Hadar typically operated their fearsome attack ships in squadrons as well. Jem'Hadar squadrons generally were comprised of three ships, (DS9: "The Jem'Hadar", "Tears of the Prophets", "Treachery, Faith and the Great River") but on occasion included only two. (DS9: "The Search, Part I", "Starship Down")