A trigger was a device that would initiate or activate a mechanism or action, such as a gun.
In 2401, Delta-7 was captured by the Vulcan Defense Forces and was being held captive in the northern foothills of Mount Tar'Hana. This company had the trigger for the Metreon Cascade, which was considered essential by the Corps for defeating the Vulcans. (PIC: "Penance")