This term is a wonderful demonstration of Unix at large being an organically grown system that was shaped and molded as its users' habits built upon each other. It is the colloquial name for a file that stores some of a user's settings or preferences for a specific application or a class thereof. The name derives from the fact that they're commonly stored in a file or directory whose name starts with a dot, located under the user's home directory. This became a convention because of the larger convention that filenames starting with a dot be treated as hidden, although there's nothing actually special about them. This was originally a simple heuristic to avoid having the special . and .. show up in every file listing.

Examples of DotFiles can be seen in SampleConfigFiles.