File extensions (e.g., ".txt", ".jpg", ".exe") identify a file's type and the program needed to open it. Operating systems like Windows or macOS often hide these extensions by default to present a simpler, cleaner file list and reduce the chance of users accidentally deleting or changing the extension, which could render the file unusable. This behavior treats the extension as internal metadata rather than a visible part of the filename.

For example, a document named "report.docx" appears simply as "report" in Windows File Explorer by default, making it less visually cluttered. Users working primarily with common document, image, or video files typically don't need to constantly see the extension, as the associated application icon usually provides sufficient visual identification of the file type in these interfaces.

While convenient for basic tasks, hiding extensions poses a security risk. Malicious actors frequently disguise executable malware files (e.g., "dangerous.exe") to appear harmless by making them look like documents, relying on the hidden extension (e.g., naming it "invoice.txt.exe" to display as "invoice.txt"). Consequently, modern operating systems increasingly default to showing extensions for critical types or allow users to easily toggle visibility in file explorer settings, balancing usability with security awareness.