In Redis, the terms "slave" and "replica" essentially refer to the same concept but are used in different versions of the software. With the release of Redis 5.0, the term "slave" was replaced with "replica", but it's important to note that their functional roles remain the same.
Both terms refer to the mechanism by which Redis achieves data replication - an essential feature for data redundancy and failover support. When "replicaof" command is issued from a Redis instance, it turns that instance into a replica (or slave in older versions) of the specified master instance. All write operations performed on the master are propagated to its replicas.
Here's a simple example of how to make one Redis instance a replica of another:
Remember, there's no difference in functionality or performance between "slave" and "replica". The change in terminology was made purely for more inclusive language use in the software industry.