Google Cloud Functions is a lightweight, event-based, asynchronous compute solution that allows you to create small, single-purpose functions that respond to cloud events without the need to manage a server or a runtime environment.
Cloud Events and Triggers
Cloud Events are things that happen in your cloud environment. These might be things like changes to data in a database, files added to a storage system, or a new virtual machine instance being created.
Events occur whether or not you choose to respond to them. Creating a response to an event is done with a Trigger. A trigger is a declaration that you are interested in a certain event or set of events. You create triggers to capture events and act on them.
Cloud Functions are the mechanism you use to respond to events. Your Cloud Functions contain the code that executes in response to a Trigger in order to process an Event.