An attack formation was a coordinated maneuver of several starships before attacking an enemy.
The Cardassian echelon was a classic Cardassian attack formation. (VOY: "Basics, Part I")
In 2369, Jasad's warship and two other Galor-class warships deployed into a standard attack formation before opening fire on Deep Space 9. (DS9: "Emissary")
Three Jem'Hadar fighters were in attack formation before engaging the USS Odyssey and several runabouts in 2370. (DS9: "The Jem'Hadar")
In 2372, several dozen Klingon ships, including the IKS Negh'Var, assumed an attack formation before attacking DS9. (DS9: "The Way of the Warrior")
While in multi-vector assault mode in 2374, the parts of the USS Prometheus were in an attack formation prior to attacking the USS Bonchune. (VOY: "Message in a Bottle")
Shortly before commencing battle during Operation Return the same year, Captain Benjamin Sisko ordered all Starfleet vessels to assume attack formation delta two. (DS9: "Favor the Bold")