Azure App Service
Azure App Services is the PaaS (Platform as a Service) hosting offering from Microsoft Azure. It is a fully managed platform for creating and hosting powerful cloud apps like Web Apps, Functions, Mobile Apps and API Apps. Here is every component that is part of the Azure App Services
Web Apps can be a simple HTML website or a complex ASP.NET running on Windows or Linux. The Web Apps marketplace offers a variety of combinations on how to directly deploy ready solutions. Joomla, Drupal, Wordpress, Web App + MySQL and so on.
App Service Environment
If the Web Apps offerings within the App Service plans are not enough for you - you have an option to provision an isolated environment with a lot more customization and scalability compared to the general Web Apps multi-tenant capabilities.
The new serverless apps that will bring the modern efficiency of paying for apps only when they execute code
You can buy or manage SSL Certificate directly from Azure Portal and get extended functionality and integration with your apps
App Service Domains
You can buy and manage Domain and their DNS zones and records directly from the Azure Portal