The published set of fares and rules an airline files (via ATPCO/GDS or regulators) that governs how a ticket can be priced and used.

Includes the fare and its rules: booking class (RBD), routing, seasonality, day/time limits, min/max stay, advance purchase, stopovers/transfers, changes/refunds penalties, baggage, and surcharges.

• Identified by a fare basis code and applied automatically by pricing systems.
• Determines what happens when you change/cancel and whether itineraries can be combined.
  Example
  “A ‘QNR7M’ economy tariff may require a 7-day advance purchase, a Saturday night stay, and charge a fee + fare difference for changes.”