The following is a list of the main types of published airfares - and are usually based on round-trip or one-way travel:

• APEX fares are discounted international fares. Such fares usually require tickets to be purchased in advance (such as 7, 14, or 21 day minimum advance purchase), and will have other restrictions - non-refundable, change fees are just a few of the possible restrictions.
• Discount Fares are fares that tend to have a smaller price tag, and are offered for a limited time (seat sales would fall into this category). They usually have a long list of restrictions such as specific travel dates, minimum and maximum stay (for example, a minimum Saturday night stay, a maximum 30 day stay), etc.
  Unlike most published fares, it is important to make sure that you are aware of the fare rules and restrictions on discount (seat sale) fares. Keep a copy of the rules because seat sale fares come and go quickly, and the rules and restrictions can be harder(sometimes impossible) to retrieve online.
  

• Excursion Fares are lower priced fares that involve restrictions like advance purchase, time of year, minimum/maximum stay, etc.
• Unrestricted, Flexible, or Full Fares are the titles given to the most expensive tickets. You pay for a ticket that allows you to refund or change the ticket as necessary for fares that can be purchased at any time, even the same day of travel.
• Joint fares are offered by airlines that have some sort of partner relationship on select routes. They essentially give a passenger a price break when you are using more than one airline to get somewhere. Joint fares have their own set of restrictions, not unlike those already mentioned for excursion and discount fares.
• A through fare is a fare to a destination reached by traveling through a gateway city. It could be combined with any of the fare types listed above, and is used to obtain a lower price when you are not simply flying from point A to point B, but are rather connecting through other points to get to your destination. If you are traveling from Atlanta to Athens via Frankfurt, you may be offered a through fare, so that instead of paying for Atlanta to Frankfurt and Frankfurt to Athens, you pay one fare for Atlanta through to Athens.

Airlines will not offer every seat on an aircraft at seat sale fares, or excursion fares. As flights fill, the least expensive fares disappear regardless of how far in advance it is. Unless you are on a full fare ticket you can be certain that there will be any number of restrictions involved with your airfare - minimum/maximum stay; time of day; weekday, weekend price differences; change fees; mileage (on through fares you may be restricted to a certain number of miles to get you to your destination), advance purchase; youth/child/senior rule differences; etc..