Azure App Service is a family of services that are provided as PaaS in Azure and help you to build apps that can be used by web and mobile clients. You can use Azure App Service with a wide range of programming languages and technologies—Node.js, Java, PHP, and, of course, .NET—and can create Web Apps, API Apps, Mobile Apps, and Logic Apps without worrying about the underlying infrastructure. 

There are many features that Azure App Service provides to assist with application lifecycle development, such as automatic deployment options, the management of application settings that can be modified based on the environment (deployment slots), easy manual and automatic scaling options, security control, monitoring, and troubleshooting utilities, to name just a few.