What is Cloud ?

The network of server's hosted over the internet is called as cloud. It can be thought similar to whenever we had to show a service coming from outside in os we used to represent it with cloud symbol.

What is Cloud Computing ?

Cloud Computing is basically delivery of IT Services like compute, storage , networking over internet.

Cloud Deployment Model ?

There are mainly four type of cloud deployment model. They are:

Public Cloud
Private Cloud
Hybrid Cloud
Community Cloud

cloud deployment type image

What is Cloud Service Model?

There are three types of Cloud Service Model. They are:

Infrastructure as a Service ( IaaS )
Platform as a Service ( PaaS )
Software as a Service ( SaaS )

In case of OnPremise (Traditional IT) we are liable to mange all the things from storage, networking, servers, os, middleware, data, application all are handled by the organization.
Whereas in case of IaaS os, virtualization, server, storage, networking are delivered to us as a service by Service Provider , whereas we are liable to manage middleware, runtime, data, application.
In case of PaaS we are responsible only to handle data, application rest all are managed by service provider. Similarly in case of SaaS all the service is handled by the service provider.
Note:
IaaS provides us the most access the underlying OS whereas in case of SaaS we have minimum access whereas we can consider pass at mid.

Essential Characteristics of Cloud Computing ?

On-demand self serviced
Broad network access
Resource Pooling
Stop Guessing Capacity
Speed and Rapid Agility
Economies of Scale
Elasticity