VMware Aria Automation Action-Based Extensibility (ABX) is a feature that allows the execution of stateless functions hosted either on-premises or in the cloud. These functions can be written in various scripting languages and are used to create reusable, parameterized actions that can be triggered by events within the Aria Automation environment. ABX is used to extend the automation capabilities of Aria Automation by integrating with external systems, performing custom tasks, and reacting to lifecycle events of resources.