Azure App Service is a fully managed Platform as a Service (PaaS) offering that enables developers to build, deploy, and host web applications, REST APIs, and mobile backends without managing servers or infrastructure. It supports multiple programming languages, including .NET, Java, Node.js, Python, PHP, and Ruby. Azure App Service provides built-in features such as automatic scaling, continuous deployment, SSL certificates, authentication, custom domains, and high availability. This allows developers to focus on application development while Azure handles the underlying infrastructure.