A cloud computing model in which network hardware is provided by an external provider and managed for you.
As with all cloud computing services, IaaS provides access to computing resources in a virtualized environment, “the Cloud,” across a public connection, usually the internet. With IaaS, however, the client is given access to virtualized components. An example of IaaS would be offering access to networking resources in a virtualized environment (the cloud) across a public connection.
See also Platform as a Service (PaaS) and Software as a Service (SaaS)