From Halopedia, the Halo wiki
Confinement fields were energy fields projected by Forerunner warships to block the movement of enemy ships. Confinement fields were also able to be projected into the interiors of enemy vessels, as evidenced by the Forerunner fleet's incapacitation of the Didact and Bornstellar Makes Eternal Lasting during the Battle of Janjur Qom. As such, they appear to be a large-scale application of constraint fields.
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