Azure Reservations help you save money by pre-paying for one-year or three-years of virtual machine, SQL Database compute capacity, Azure Cosmos DB throughput, or other Azure resources. Pre-paying allows you to get a discount on the resources you use. Reservations can significantly reduce your virtual machine, SQL database compute, Azure Cosmos DB, and other resource costs up to 72% compared to pay-as-you-go prices. Reservations provide a billing discount and don't affect the runtime state of your resources. For more information see What are Azure Reservations?

Following are some useful links to know more about Microsoft Azure RI: