What are the salient features of cloud computing?

What will be an ideal response?

Answer: Peter Mell and Timothy Grance of the National Institute of Standards and Technology (NIST) define cloud computing as "a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction." According to Mell and Grance, the cloud model has five essential characteristics:
On-demand self-service. Users can automatically access applications and storage space whenever they need them.
Broad network access. Capabilities are available over the network and accessed through standard mechanisms that promote use by a wide range of platforms, including mobile phones, laptops, and PDAs.
Resource pooling. The provider's computing resources are pooled to serve multiple consumers, with different physical and virtual resources dynamically assigned and reassigned according to consumer demand.
Rapid elasticity. Capabilities can be rapidly and elastically provisioned, in some cases automatically, to quickly scale out, and they can be rapidly released to quickly scale in. To the consumer, the capabilities available for provisioning often appear to be unlimited and can be purchased in any quantity at any time.
Measured service. Resource usage can be monitored, controlled, and reported, providing transparency for both the provider and consumer of the utilized service.