What is database replication and what are the different types?

Replication copies data across multiple database servers. Types: Master-Slave (writes to master, reads from slaves - read scaling), Master-Master (writes to any master, complex conflict resolution), Synchronous (waits for replicas - consistency but slower), Asynchronous (doesn't wait - faster but potential data loss). Benefits: read scaling, high availability, geographic distribution. Challenges: replication lag, conflict resolution, consistency guarantees.