A cloud service is any resource that is provided over the Internet. The most common cloud service resources are 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. PaaS refers to the delivery of operating systems and associated services over the Internet without downloads or installation. 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. SaaS, PaaS and IaaS are sometimes referred to collectively as the SPI model.
Cloud services are the same thing as Web services. However, the term cloud services has been more commonly used as cloud computing has become more pervasive.
See also: XaaS (anything as a service)