Here I listed 5 essentials characteristics of cloud computing :
On demand self-services : Computer services such as email, applications, network, or server service can be delivered without needing human interaction with each service provider.
Broad network access : Cloud capabilities are accessible over the network and accessed via standard mechanisms that support the use of heterogeneous thin or thick client platforms such as mobile phones, laptops, and PDAs.
Resource pooling : The computing resources of the providers are pooled together and use the multiple-tenant model, with different virtual and physical resources dynamically assigned and reassigned depending on the consumer demand for serving multiple consumers.
Rapid elasticity : Cloud services can be rapidly and elastically provisioned in order to quickly scale out and rapidly released in order to quickly scale in. The capabilities that are present for provisioning generally appear unlimited to the consumer, and can be bought in any quantity at any time.
Measured service : The resource usage of cloud computing can be measured, controlled, and reported and provides transparency for the provider and consumer of the utilized service. Cloud computing services make use of a metering capability that controls and optimizes the use of resources.