PaaS

PaaS stands for "Platform as a Service", and was first proposed by salesforce.com in 2007. It refers to a form or business model in which the platform (development environment such as OS and middleware) necessary for building and running software and applications is provided as a service that can be used over the Internet.
Typical services include Google App Engine, Salesforce Platform, Kintone, AWS Lambda, and AWS Elastic Beanstalk.

SaaS is introduced as one of the cloud services that provide services over the Internet, together with Iaas (infrastructure provision) and Saas (service and function provision).
SaaS is a form of providing a system developed by a company as a service over the Internet, while PaaS provides a platform that users can use to build their own systems and develop their own applications.