What is Platform as a service PaaS?

PaaS make it easy to develop, build, test and deploy applications written in some language. Not all PaaS offers support for all languagse and there are restrictions in choice of frameworks and language. Some restricts deployment to a signle cloud. The key and reason to use PaaS is developers agility. There is nothing between your idea and the application to be implemented and you should develop and implement your idea to application fast. Then idea is to write your application once and test , scale and deploy to production.