It is the recent sold price for the same card at the same grade — completed sales, not asking prices, and that distinction matters more than anything else on this page. Anyone can list a card at any number; only a sale proves what it is worth.
It comes from one of three places, and the listing says which: Card Ladder, which aggregates public sold listings; the median of the last three completed sales of that exact card at that exact grade, published so you can check it yourself; or a manual appraisal when no usable sale exists. We take the median rather than the average, because one odd sale moves an average a long way and a median hardly at all.
Auctions and buy-it-now sales both count. An auction with real bidding is the truest price a card has, so excluding them would throw away most of the evidence on anything expensive. We record what the buyer actually paid — buyer’s premium included, shipping and tax excluded — and we ignore any sale where the price is hidden, where nobody bid against the opening, or where a lot was broken up into per-card guesses.
Each comparable shows the date it is drawn from. If we do not have a recent sale for that card at that grade, the listing shows no comparable at all. We would rather publish nothing than present a number from four months ago as if it were today.
The comparable is context, not a promise. Sometimes our price sits above it — for a scarce grade, or a card we paid up for — and you can see that plainly, which is the intended behaviour.