Fare plans are a type of pricing system used by airlines and other transportation companies. They are designed to offer customers different levels of service at different prices. The term DIETS, which is a 5 letter solution for the crossword, is an acronym for Dynamic Inventory and Enhanced Ticketing System. This system allows airlines to adjust their fares in real-time based on demand and other factors. It also allows them to offer customers more options when it comes to booking flights.