what is meant by cloud computing? give some examples
Cloud Computing is an overarching category. You've got at least 3 distinct segments in this evolving market:
IaaS: Infrastructure as a Service e.g. Amazon EC2
PaaS: Platform as a Service e.g. Google AppEngine
SaaS: Software as a Service e.g. Salesforce
There is an emergent category also:
DaaS: Database as a Service e.g. Amazon RDS, Microsoft SQL
In short, Cloud Computing relates to computing resources available through the WEB. Of course some folks will disagree to some extent with this definition but it can't be all wrong :-)
Simply put, cloud computing combines CPU virtualisation, software as a service, and utility computing.
Utility computing refers to treating computing services as a utility that can be delivered like you would deliver water or gas. Easy to turn on, turn off, or increase the flow. This was enabled by effective CPU virtualisation, and the tools to manage these virtual CPUs in a zero-touch manner. Add on top of that, software as a service, and you have cloud computing. Some services are very barebones such as Amazon S3 storage, and others are more complex like salesforce.com CRM.