Core update

What it means

A core update is a broad change to how search ranking systems assess pages, announced in advance and rolled out over a period of days or weeks. It is not aimed at any particular site. What changes is the judgement of which pages best answer a query, and sites move up or down as a consequence of that reassessment rather than as a punishment for anything specific.

Update and penalty are different things

A penalty is a targeted action in response to a specific violation, and it comes with a notification. A core update is a change in the weather. Sites lose substantial traffic in core updates while having done nothing against any guideline, which is cold comfort but important to understand, because the remedies are entirely different. Looking for a rule you broke after an update is usually looking for something that does not exist.

What a buyer reads into one

A buyer prices the traffic in front of them. A site that halved in a recent update is worth a multiple of what it now earns, not of what it earned before, and the seller's account of an imminent recovery carries no weight without evidence. More significantly, a site that has moved sharply in successive updates is demonstrably sensitive to them, and that volatility reduces the multiple even when the current numbers are healthy.

What recovery looks like

Slow, partial and dependent on real improvement to the pages that lost ground. Recovery frequently arrives only when a later update takes effect, which means months rather than weeks, and a proportion of sites never regain their previous position. If you are selling into this situation, the honest approach is to disclose it, show the work done since, and price on the current figures. Buyers discover it in the data regardless.