A trigger is a set of actions that are executed automatically once certain conditions are met. For example, a trigger can modify issue parameters, leave an automatic comment, or send an HTTP request if a status changes or a specific user subscribes to an issue.
You can use triggers to automatically pick assignees for issues, send email notifications when issues are created from user requests, or send notifications to messengers from Tracker.
Each queue has its own set of triggers. Triggers are executed in the same order they were listed in queue settings. However, you can manually change the trigger order if necessary.