All 7 Always On Availability Groups questions
More in Always On Availability Groups
What is an Always On Availability Group in SQL Server, and what problem does it solve? What is the difference between automatic failover and manual failover in an Always On Availability Group? What is an availability group listener, and why is it important for applications connecting to an Always On Availability Group? What are the licensing and edition requirements for using Always On Availability Groups in SQL Server? How do you decide between synchronous commit mode and asynchronous commit mode for a specific replica in an Always On Availability Group? How would you plan a disaster recovery strategy that combines Always On Availability Groups across multiple data centers with regular backups?
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What is the difference between the primary replica and secondary replicas in an Always On Availability Group?

Beginner

Answer

The primary replica is the active database that handles all the read and write operations from your applications, while secondary replicas hold a continuously updated copy of that data and can optionally be used for read only reporting queries, backups, or as a standby ready to take over if the primary fails.
-- Read only routing lets reporting queries run against a secondary replica
-- instead of adding extra load to the primary
Real-world example A company offloads its heavy reporting queries to a secondary replica, keeping the primary replica free to handle the application's regular transactional workload without slowing down.

Common follow-ups: Can you write data directly to a secondary replica?;How much delay is typical between the primary and a secondary replica?

Backup & Recovery;Query Optimization & Plans
All 7 Always On Availability Groups questions