Clustered hosting is the most recent way of hosting the website. A cluster is a group of computers or servers, whose collective computational power gives a service.
Clustered hosting involves distributing the website across multiple servers, like layers. Each layer performs its own individual task, so one for web, one for logging, one for databases etc. This has one significant advantage, if one server goes down the other servers in the cluster will pick up the load, assuring that your site stays online.