A triggered ability is an ability that automatically goes on the stack without a player playing it or paying for it. Triggered abilities are written in one of 2 forms:
- At : The trigger condition is when the time is reached.
- When <event>, <action>: The trigger condition is when the event occurs.
In either case, when the trigger condition happens the action is put on the stack as an instantaneous effect (See instantaneous effect for information about ordering on the stack).