What is the difference between failover and clustering?

Failover is having redundancy built into the environment, so that if a server fails, another server takes its place.

Failover can be done in more than one manner, including by clustering. To use clustering for failover, configure a second server in the environment on a different computer than the primary server to handle some of the processing. When the primary server fails, the second server would continue to process, thus acting as a backup to the primary server (active/active approach).

Another failover method is to have additional hardware that is being used as a backup for this purpose but is not being used while the primary server is up and running (active/passive approach).