Definition: The word `files` in PHP refers to files or directories that are located on a server's filesystem. A file or directory can be considered a file if it contains code, data, or metadata. For example, a `file.php` file could contain HTML code, CSS stylesheets, JavaScript code, or other markup that is used within the document. On the server-side, files are typically accessed by clients using HTTP requests, which return a response containing the contents of the file. For instance: ``` GET /files.php HTTP/1.0 ``` This request would return the contents of `/files.php` as a response code 200. ```