Replication is the process of copying/moving data between 
databases on the same or different servers. SQL Server 
supports the following types of replication scenarios: 

Snapshot replication 
Transactional replication (with immediate updating 
subscribers, with queued updating subscribers) 
Merge replication 

Database replication is the creation and maintenance of 
multiple copies of the same database.

In most implementations of database replication, one 
database server maintains the master copy of the database 
and additional database servers maintain slave copies of 
the database.

Database writes are sent to the master database server and 
are then replicated by the slave database servers.

Database reads are divided among all of the database 
servers, which results in a large performance advantage due 
to load sharing. 

In addition, database replication can also improve 
availability because the slave database servers can be 
configured to take over the master role if the master 
database server becomes unavailable.