https://learn.microsoft.com/en-us/azure/azure-functions/functions-overview
A function is the primary concept in Azure Functions. A function contains two important pieces - your code, which can be written in a variety of languages, and some config, the function.json file.
Every function has one and only one trigger. The runtime uses this config file to determine the events to monitor and how to pass data into and return data from a function execution.
Binding to a function is a way of declaratively connecting another resource to the function.
A function app provides an execution context in Azure in which your functions run: its the unit of deployment and management for your functions.