There's almost no end to the the different types of fares and fare codes that business travelers can encounter when booking an airline ticket. One of the cleanest (and generally most expensive) such fares is an unrestricted fare.
Unrestricted fares are airline (or other transportation) fares that do not have restrictions, such as a Saturday night stay, a 14 day advance purchase, or a specific number of nights stay requirement. Many unrestricted fares are refundable.
Examples of unrestricted fares are typically full-fare coach tickets or first-class tickets. Such tickets are usually fully refundable with complete flexibility. Of course, they're not the cheapest fares. For that, it's best to look for ways to get the best air fares.