Azure App Service vs Azure Functions: What are the differences?
Developers describe Azure App Service as "Build, deploy, and scale web apps on a fully managed platform". Quickly build, deploy, and scale web apps created with popular frameworks .NET, .NET Core, Node.js, Java, PHP, Ruby, or Python, in containers or running on any operating system. Meet rigorous, enterprise-grade performance, security, and compliance requirements by using the fully managed platform for your operational and monitoring tasks. On the other hand, Azure Functions is detailed as "Listen and react to events across your stack". Azure Functions is an event driven, compute-on-demand experience that extends the existing Azure application platform with capabilities to implement code triggered by events occurring in virtually any Azure or 3rd party service as well as on-premises systems.
Azure App Service and Azure Functions are primarily classified as "Platform as a Service" and "Serverless / Task Processing" tools respectively.