Glossary Entry: Extension

An extension is the part of a filename after the last period. These are typically used to tell the operating system what program is used to open the file.

For example, the extension of the file named my_story.txt is ".txt", which is the extension commonly used by plain text files.

Some operating systems can be configured to hide extensions from the user. This effectively protects them, as the user cannot change that part of the filename.