In bidirectional replication, the source and destination media can play interchangeable roles. Bidirectional replication contrasts with unidirectional replication, in which the source and destination media cannot be transposed; data goes in only one direction.
In general computer and networking practice, replication is simply the process of copying data. In networks, files such as databases are often replicated on multiple computers or servers. On the Internet, Web sites are commonly replicated on so-called mirrors.