Batch renaming file extensions means changing the suffix (like .txt, .jpg) on multiple files simultaneously. Unlike manually renaming each file, this process uses tools or commands to automate changing only the extension part of filenames across a selected group. It's efficient when you need to convert a set of files to use a uniform or different format indicator, such as changing temporary .tmp files to their final format, without altering the core filename itself.

This is commonly done using a computer's file explorer: in Windows, select files, press F2, change one extension, and all selected files update. On macOS, select files in Finder, right-click, choose "Rename X items," then set the format to "Name and Extension" and type the new extension. Advanced users employ scripting (PowerShell, Bash) or dedicated file management software to handle complex renaming rules across thousands of files, useful in data processing pipelines, photography workflows, or software development.

The main advantage is significant time savings over manual renaming and ensures consistency. Key limitations include the risk of accidentally making files unopenable if the wrong extension is used and the inability to rename open/locked files. Always back up files before large batch operations. Misusing extensions can mislead users or software about file contents, so it's crucial to match the extension to the actual file format. Scripting offers powerful automation for future needs.