Promotion expiry is the date when a temporary offer ends and its terms may change. In security-sensitive systems, expiry dates are often attached to discounts, trial accounts, coupon codes, access tokens, and time-limited permissions. Once the promotion expires, the system may stop accepting the offer, switch to standard pricing, or require re-validation.
This matters in cyber security because expiry creates a control boundary. Defenders use expiration to limit how long credentials, links, or privileges remain usable, reducing the window for abuse. Attackers also exploit expiry by sending urgent messages that pressure users before a deadline, or by abusing stale promotional rules that were not fully removed. Good practice is to verify the exact end date, the resources covered, and what changes after expiry so users and systems do not rely on outdated terms.