A trigger is an event that starts a task. The system comes with time and file change triggers pre-installed.
A task supports multiple triggers - no matter the trigger type - but do not necessarily need a specific trigger. Signals for starting a task will be ignored if a task is already running. Another iteration of the task can only be started if the previous one did finish.
A task can always be triggered manually using the web interface or web API. Tasks can also be triggered using the Next Task Action.
Note: Triggering a task manually using the web interface or the web API does not take any triggers into account and immediately starts running the jobs.