From Halopedia, the Halo wiki
A timelock is a temporal stasis field in which the passage of time is brought to a standstill through sophisticated higher-dimensional manipulation. Both the Forerunners and prehistoric San'Shyuum possessed timelocking technology. Prehistoric humans placed a form of timelock—a piece of ancient San'Shyuum technology also known as a time bolt—on the Primordial's prison beneath Charum Hakkor's arena to prevent it from escaping. According to the Didact, this measure was almost as effective as Forerunner technology.
The Forerunners had an advanced grasp of slipspace bubbles and used variations of the timelock concept for a number of purposes. One of these was the slipspace field pod, a stasis pod capable of suspending its occupants in time. Forerunner Durances were traditionally timelocked after the last impressions of a deceased Forerunner were enclosed within. The Forerunners were also capable of creating reverse timelock fields, in which time passed at a vastly more rapid pace than within normal space. The IsoDidact used a prison cage containing a reverse timelock to execute the Primordial on Installation 07, forcing the being to disintegrate via the process of entropy through the artificially-induced passage of a billion years.
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