Actually, it would most likely be simply a cluster as opposed to cloud hosting.
Basically, you locate certain services on each VPS and have them work together. For example, you might have one server that functions as a MySQL server, another which handles the DNS, and the third which actually hosts the files for the site. There are a wide range of cluster configurations, but the idea is to devote more power to each setup. Typically, this is used for active websites (can be as few as a single website).
Cloud hosting is a bit different a bit more complex.