Privilege bracketing is the practice of limiting temporarily increased permission levels to the briefest possible time period.
When some task requires greater privileges for a user (or some other entity, such as a program or process), controls ensure that permission levels are not raised until the last possible moment and that they revert to the former level as soon as the need has passed.
Privilege bracketing can be controlled by software or mandated by policies. In a personal computing context, you might log on to an administrative account when necessary for some task and immediately revert to a lower-level account as soon as that task is complete.
Privilege bracketing is related to the principle of least privilege (POLP).