What is citation decay?
Citation decay is a lasting drop in how often a URL is cited for a fixed prompt set, after you account for ordinary run-to-run variation. One missing citation on one day is not decay. Decay is a decline that remains when you keep the prompts, engines, and counting rules the same.
Why it matters for AI visibility
AI answers are unstable. A page can be cited on Monday and absent on Tuesday because the engine retrieved a different set, not because the page failed. Calling every dip decay causes teams to rewrite pages that do not need it. Real decay still matters: a source that used to support your category answers can be replaced by fresher reviews, a changed product, or a page that no longer matches the question. You only see it in a series. Chart whether each URL is cited on each check, and compare a recent window with an earlier one of the same length. Look for a drop that survives the usual noise. Then read the answers that stopped citing you and see which sources took the place. Refresh the page when the substance is stale. Changing only the visible date, without a real edit, is not a remedy you can honestly credit.
Example
A guide is cited on most weekly checks for a quarter, then on almost none of the checks for the next month, while a newer comparison starts appearing for the same prompts. That pattern is worth calling decay. A single week with no citation, between weeks that have it, is not.
Related terms
Prompt tracking produces the series you need. An AI citation is the event that becomes less frequent. Earned media can decay too, when a third-party page that used to be cited is no longer retrieved. Do not treat a one-day gap as a trend.