Applicable fare

An applicable fare is a fare with a price locked in at the moment a ticket is issued, after all fare-construction rules and surcharges have been applied. 

That fare governs the ticket regardless of later public price changes—no refunds or extra charges follow simply because public prices moved. 

For example, a traveler books a ticket on March 1 for travel starting April 1 at $120, which is the applicable price at the time of issuance. If, on March 10, the airline reduces the published fare for April 1 travel to $100, the passenger is not entitled to a $20 refund.

However, if the traveler modifies the departure date, so the ticket is re-priced, they could receive a $20 refund of the difference because the ticket was reissued under a lower applicable fare.