Fare bucket refers to availability of a fare at published pricing. The only time that fares affect seat availability is for non-status passengers. Elite passengers can select any seat in the economy cabin on any fare. Non-elite passengers are restricted to the non-preferred seats. The exception occurs when non-elites are traveling on a full-fare economy (Y or B class) which allows them access to the Preferred seats. Check out the tutorials in the mileage run forum to learn all about fare buckets.