An event or action that causes a person to engage in a specific behavior (can be a repeated behavior but does not have to be). In behavioral design, triggers can also be a term to describe an action that causes the release of the neurotransmitter dopamine (and other chemicals too) into the neural space.
The general concept of
triggers goes by many names: prompts, cues, calls to action, and
so on. The idea is similar: A trigger is something that tells people
to perform a behavior now. Fogg defines three types of triggers: sparks (trigger that motivates behavior aligned to the 3 core motivators of fear/danger, sex, and hunger), facilitators (trigger makes behavior
Easier), and signals (a trigger that indicates or reminds)