Azure Reservations for the Azure SQL Database service became available earlier in August 2018 (see our blog post here: http://bit.ly/2KROzpp). If you want to understand more about how the reservation discount is applied automatically to running Azure SQL Databases then this is a useful article: http://bit.ly/2vX61UR.
Microsoft announce the General Availability of Azure SQL Database Reserved Capacity for single and elastic pool databases. If you’re familiar with Reserved Instances for virtual machines, then this is the same kind of thing for the Azure SQL Database service. Essentially, you can save money by prepaying for SQL Database vCores for a one or three-year term. In addition, you can bring your own SQL Server licences (either via active SA or the new Server Subscriptions) for an even more cost-effective solution.
SQL Database Reserved Capacity shares other similarities with Reserved Instances too: a Reservation can be assigned to either a single Azure Subscription or shared, and there’s vCore Size Flexibility as well where the Reservation can be applied dynamically to any databases and elastic pools within a performance tier and region.