Fare bucket (booking class)

The single-letter inventory classes airlines use to manage how many seats sell at each price — J, C, D, Z and I are common business-class buckets. The cabin is the same; the bucket determines price, change rules and mileage accrual. When a website says business class is "sold out", it usually means the cheap buckets are closed while expensive ones remain. Negotiated fares book into specific buckets, which is why specialists can often ticket flights the public engines price absurdly.