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The term cloud services is a broad category that encompasses the myriad IT resources provided over the internet. The expression may also be used to describe professional services that support the selection, deployment and ongoing management of various cloud-based resources.

The first sense of cloud services covers a wide range of resources that a service provider delivers to customers via the internet, which, in this context, has broadly become known as the cloud. Characteristics of cloud services include self-provisioning and elasticity; that is, customers can provision services on an on-demand basis and shut them down when no longer necessary. In addition, customers typically subscribe to cloud services, under a monthly billing arrangement, for example, rather than pay for software licenses and supporting server and network infrastructure upfront. In many transactions, this approach makes a cloud-based technology an operational expense, rather than a capital expense. From a management standpoint, cloud-based technology lets organizations access software, storage, compute and other IT infrastructure elements without the burden of maintaining and upgrading them.

The usage of cloud services has become closely associated with common cloud offerings, such as software as a service (SaaS), platform as a service (PaaS) and infrastructure as a service (IaaS).

SaaS 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. Examples include G Suite -- formerly Google Apps -- Microsoft Office 365, Salesforce and Workday.

PaaS refers to the delivery of operating systems and associated services over the internet without downloads or installation. The approach lets customers create and deploy applications without having to invest in the underlying infrastructure. Examples include Amazon Web Services' Elastic Beanstalk, Microsoft Azure -- which refers to its PaaS offering as Cloud Services -- and Salesforce's App Cloud.

IaaS involves outsourcing the equipment used to support operations, including storage, hardware, servers and networking components, all of which are made accessible over a network. Examples include Amazon Web Services, IBM Bluemix and Microsoft Azure. SaaS, PaaS and IaaS are sometimes referred to collectively as theSPI model.

Cloud services that a service provider offers to multiple customers through the internet are referred to as public cloud services. The SaaS, PaaS and IaaS providers noted above may all be said to be providing public cloud-based services.

Private cloud services, in contrast, are not made generally available to individual or corporate users or subscribers. Private cloud-based services use technologies and approaches associated with public clouds, such as virtualization and self-service. But private cloud services run on an organization's own infrastructure and are dedicated to internal users, rather than multiple, external customers.

The second sense of cloud services involves professional services that enable customers to deploy the various types of cloud services. Consulting firms, systems integrators and other channel partners may offer such services to help their clients adopt cloud-based technology.

In this context, cloud services might include any or all of the following offerings: cloud-readiness assessment, application rationalization, migration, deployment, customization, private and public cloud integration -- hybrid clouds -- and ongoing management. Companies specializing in cloud services have become an attractive acquisition target for large IT services providers -- Accenture, IBM and Wipro, for instance -- that seek expertise in cloud consulting and deployment.

Cloud services are sometimes deemed synonymous with web services. The two fields, although related, are not identical. A web service provides a way for applications or computers to communicate with each over the World Wide Web. So, web services are generally associated with machine-to-machine communications, while cloud services are generally associated with scenarios in which individuals or corporate customers consume the service -- users accessing office productivity tools via a SaaS-based application, for example.

Some web services, however, may be closely intertwined with cloud services and their delivery to individuals and organizations. Cloud services, for instance, often use RESTful web services, which are based on representational state transfer (REST) technology. REST is viewed as providing open and well-defined interfaces for application and infrastructure services.

See also: XaaS (anything as a service)

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What is cloud services? - Definition from WhatIs.com