The waitlist is a computerized program that allows you to be placed on a list and wait for a specific class of service to become available in advance of going to the airport and taking your flight. If the desired class of service becomes available you will pay the usual price in order to be confirmed, as well as any change fee if you have an existing confirmed ticket. Whether or not a waitlist is permitted will depend on the airline and fare rules. Often the deeply discounted fares do not allow waitlists, but intermediate and higher fares usually do.
Stand-by is the ability to board a different flight on the same airline and on the same day for which you are holding a confirmed ticket. Each airline has its own policies regarding which fares, flights, and passengers are eligible for stand-by. Typically, requests to be added to the stand-by list must be done either at the airport or sometimes via online check-in, and time limits can range from no more than 3 hours in advance to up to 24 hours. Costs range from free to about $75 domestically for U.S.-based carriers. If space is available after all confirmed passengers have been seated the stand-by passengers will be boarded.
