This both are two high availability techniques. Data base mirroring is a technique by which we can secure our database server.
for example:-SQL Server database mirroring is a disaster recovery and high availability technique that involves two SQL Server instances on the same or different machines. One SQL Server instance acts as a primary instance called the principal, while the other is a mirrored instance called the mirror.
Database replication:-In replication, data and database objects are copied and distributed from one database to another.