Platform as a service (PaaS) is a concept that describes a computing platform that is rented or delivered as an integrated solution, solution stack or service through an Internet connection.
The solution stack may be a set of components or software subsystems used to develop a fully functional product or service, such as a web application that uses an OS, web server, database and programming language.
More generically, the solution stack may deliver an OS, middleware, database or application.
PaaS evolved from software as a service (SaaS), which uses the Internet to host software applications.
PaaS is the center of the five layers of cloud computing.
The two layers above PaaS are the client (hardware and software) and application (including SaaS) layers.
Below the PaaS are the infrastructure – including infrastructure as a service (IaaS) - and server (hardware and software) layers.
The PaaS service delivery model allows a customer to rent virtualized servers and associated services used to run existing applications, or to design, develop, test, deploy and host applications.
PaaS offerings include a variety of services and service combinations spanning the application development lifecycle.
Typical service features include source code control and tracking, versioning, testing and build process management tools.