An ACTION file is a file written in Xcode and used by Automator, a program for creating automations in macOS. It contains a specific action that can be combined with other actions to create an automated process (these processes are saved as .WORKFLOW documents).

Actions are used to automate tasks in macOS, typically with Finder or another program. The actions are especially helpful for repetitive tasks, such as batch creating sequential folders, editing images in Photoshop, or deleting files. ACTION files may be saved in one of the following folders: 1. /System/Library/Automator The most common location of ACTION files in OS X. 2. /Library/Automator The location for ACTION files installed by an administrator but available on all the accounts of the computer. 3. ~/Library/Automator The location for ACTION files available for specific users.