The Buy Box on Amazon is the panel on a product page that holds the "Add to Cart" + "Buy Now" buttons. It is shown to the seller that Amazon's algorithm picks as the default option among all sellers offering the same ASIN.
Losing the Buy Box to a competing seller drops the brand's conversion + ad-attributed revenue from that ASIN to near zero. The Buy Box-eligibility factors include: price (competitive vs MAP), fulfilment method (FBA usually wins over FBM), seller rating, inventory health, response-time metrics.
The discipline: daily Buy Box-share monitoring per high-revenue ASIN, MAP policy + enforcement against authorised resellers, repricer running to the MAP floor + defensible margin, and FBA preference for top-tier ASINs. Buy Box-share below 90 percent on a high-revenue ASIN triggers investigation, not optimisation.