Final answer:
The expiration timeout refers to the duration before a system action is automatically initiated if not addressed within a specified period.
Step-by-step explanation:
Depending on the action, the expiration timeout typically refers to the duration before the action is automatically taken. This is common in systems where an action must occur after a certain period, and if not addressed within that period, it defaults to a prescribed behavior. This could include the deactivation of a session due to inactivity, auto-saving a document after a set time, or any number of other automated system tasks.