The Imperial Interdictor is a warship used to hold ships in one area.
The gravity projectors on an Interdictor are often sucking up the ship's energy as they are used. With them on, a strong attack can take down the shields, such as when Rogue Squadron jumped in-system next to a blockade runner being attacked by an Interdictor.
The weaponry of an Imperial Interdictor is often removed or greatly diminished to make room for the gravity projectors. The projectors of an Interdictor greatly interfere with weaponry and shield power. Because of this, an Interdictor has often had to have a guard or two in order to defeat enemy Star Destroyers. Imperial Interdictors also are usually deployed to get rid of weak defenders and pirate nests.