Platform as a Service (PaaS)
is a cloud computing service that uses virtualization to offer an application-development platform to developers or organizations. This platform includes computing, memory, storage, database, and other app development services. PaaS technology offers a company virtual infrastructure, such as data centers, servers, storage and network equipment, as well as an intermediate layer of software, which includes tools for building apps.
Software as a Service (SaaS)
is a software licensing model, which allows access to software on a subscription basis using external servers. SaaS allows each user to access programs via the internet instead of having to install the software on the user's computer. SaaS has many business applications including file sharing, email, calendars, customer retention management, and human resources.
Infrastructure as a Service (IaaS)
provides compute, memory, storage, networking and related software, such as operating systems and databases, as a cloud service to replace traditional on-premises data center infrastructure. This solution provides the end user with flexibility when it comes to hosting custom-built apps or standard software while also providing a general data center for storage.