Trigger
A trigger is the event that starts automated work: a message arriving, a record changing, a meeting ending, a schedule coming round.
Triggers are what move AI from something you visit to something that runs. Instead of a person noticing a condition and asking, the system watches for it. The event also carries the context the work needs, which is why a well-chosen trigger often produces a better result than the same request typed by hand.
Choosing them is mostly an exercise in restraint. A trigger that fires on everything produces output nobody reads; one that fires on a genuinely meaningful condition produces work people come to rely on. The other half of the design is what the run is allowed to do on its own once it starts, which is a governance question rather than a trigger one.