Injector ports were components that allowed the controlled infusion of matter and antimatter, leading to a successful reaction that powered up a warp engine, making it operational. This was standard procedure upon undocking or leaving a drydock.
In 2153, T'Pol suggested that Sim replace the A-3 injector port of Enterprise NX-01's engineering section when he expressed a desire to spend his last hours of life in engineering. (ENT: "Similitude")
In 2375, the antimatter injector ports on the USS Defiant were opened, after the dilithium matrix had been aligned and calibrated, when the ship was about to leave Deep Space 9 for the Second Battle of Chin'toka. (DS9: "The Changing Face of Evil")