Azure Functions allow developers to write small pieces of code, or "functions", that can be run in the cloud and are triggered by events. Functions can be triggered by common data sources like Azure Blob storage, queues, and tables. Functions code can be written in C#, F#, Node.js, or Python and bindings define how functions connect to triggers and external data sources. Functions can be tested locally and deployed to Azure to be run on an event-driven schedule.