Cloud-Service is all about Hardware or software provided to you as a service and accessible through the internet.
There are basically 3 types of cloud service
Infrastructure as a Service (IaaS)
Organization outsources the equipment used to support operations, storage, hardware, servers and networking components. The service provider owns the equipment and is responsible for housing, running and maintaining it. The client typically pays on a per-use basis.
Some popular Vendors of Infrastructure as a Service (IaaS) :Amazon, AT & T, HP,Rackspace
Software as a Service (SaaS)
It is a software distribution model in which applications are hosted by a vendor or service provider and made available to customers over a network, typically the Internet.
Some popular Vendors of Software as a Service (SaaS) : Salesforce, LinkedIn,ServiceNow
Platform as a Service (PaaS)
Platform as a Service allows users to create software applications using tools supplied by the provider and also user can provide services over the internet.
Some popular Vendors of Platform as a Service (PaaS) : Google App Engine, Amazon web services, Salesforce, Windows Azure , IBM Smart Cloud.