Introduced in Microsoft SQL Server 2012, AlwaysOn Availability Groups feature is a high-availability and disaster-recovery solution that provides an enterprise-level alternative to database mirroring.
"'AlwaysOn Availability Groups' maximizes the availability of a set of user databases for an enterprise. Deploying AlwaysOn Availability Groups involves creating and configuring one or more availability groups. Each availability group is a container for a discrete set of user databases, known as availability databases, that fail over together. An availability group can have multiple possible failover targets (secondary replicas). Moreover, you can configure secondary replicas to support read-only access to secondary databases and for performing backups on secondary databases," explains Microsoft.