|Some vessels, as well as structures on planets, have the ability to stop all enemy jump drive functions within 1,000 gu of their position.
Running such a vessel is a highly respectable activity in any fleet's operation, as the inability of enemy vessels to escape from a skilled Interdictor pilot can easily turn an outnumbered fleet into the victor.
However, this threat goes both ways... when jumping, your course line will not indicate any danger by an interdictor field. If you hit one, your ship will stop its jump and be at the mercy of any enemy defenses or ships nearby.
Therefore you should always be mindful of the presence, or the need, of the Interdictor.