In starship classification, an escort vessel was a starship whose primary purpose was to accompany and protect other vessels.
In 2154, two Xindi-Reptilian warships escorted Degra's ship during the initial testing of the Xindi test weapon in the Calindra system. (ENT: "Proving Ground")
In 2367, a radical faction based on the Beta moon of Peliar Zel sent a ship claiming to be an escort vessel to intercept the Federation shuttlecraft Hawking. (TNG: "The Host")
The Defiant-class Federation starship, originally developed to counter the Borg, was officially classified as an escort vessel, but was unofficially a warship. (DS9: "The Search, Part I")
In 2372 during the Klingon-Cardassian War, Starfleet provided escort ships for Cardassian convoys carrying humanitarian relief supplies. (DS9: "Rules of Engagement")
In an alternate timeline, Admiral William Riker berated Worf for allowing the USS Pasteur to enter the former Romulan Neutral Zone without an escort. (TNG: "All Good Things...")