On-demand Computing is the latest model in enterprise systems. It is related to Cloud computing. It means IT resources can be provided on demand by a Cloud provider.
In an enterprise system demand for computing resources varies from time to time. In such a scenario, On-demand computing makes sure that servers and IT resources are provisioned to handle the increase/decrease in demand.
A cloud provider maintains a poll of resources. The pool of resources contains networks, servers, storage, applications and services. This pool can serve the varying demand of resources and computing by various enterprise clients.
There are many concepts like- grid computing, utility computing, autonomic computing etc. that are similar to on-demand computing.
This is the most popular trend in computing model as of now.