Many cloud web hosts offer unlimited monthly data transfers, so other factors may help you decide which service is best for your business. That said, if you're interested in "unlimited" anything, no matter if it's data or storage, be sure to read the tiny print to make sure that there aren't any surprises. In other words, make sure your definition of unlimited matches the hosting service's definition. They can be two very different things.
Cloud hosting is an alternative to hosting websites on single servers (either dedicated or shared servers) and can be considered as an extension of the concept of clustered hosting where websites are hosted on multiple servers. With cloud hosting, however, the network of servers that are used is vast and often pulled from different data centres in different locations.