The gradual decline in a page's organic traffic over time as the content goes stale, competitors publish fresher takes, search intent shifts, or Google's algorithms re-evaluate it. Decay is normal — even a perfectly good article will lose ground after a year or two unless updated. The standard remedy is "content refresh": update statistics, add new sections covering changes in the field, reflect current product naming and screenshots, and re-publish under the same URL. Tracking decay is straightforward in GSC: filter to pages losing clicks quarter-over-quarter and prioritise the highest-value losers.