What is a File?

A file is a computer resource for recording data, primarily identified by its file name, and usually having a file extension that identifies the type of file it is. Files can be documents, programs, or other types of data. For example: notepad.exe is an executable file; data.json would be a JSON file; logo.psd would be an Adobe Photoshop document.

A sampling of file types:

Text files: .txt, .html, .xml, .rtf
Server Side Scripting files: .php, .jsp, .asp
Web Image files: .gif, .jpg, .png, .svg, .webp
Audio files: .mp3, .ogg, .au
Video files: .mp4, .avi
Application files: .psd (Adobe Photoshop), .pdf (Adobe Portable Document File), .ai (Adobe Illustrator), .doc (Microsoft Word)

The file extension is often hidden on some platforms and you may need to make some changes to your operating system setting to get them to display.

Mac

In the Finder on your Mac, choose Finder > Preferences, then click Advanced. Select or deselect Show all filename extensions.

Windows

Open File Explorer; if you do not have an icon for this in the task bar; click Start, click Windows System, and then File Explorer.
Click the View tab in File Explorer.
Click the box next to File name extensions to see file extensions.
Click the box next to Hidden items to see hidden files.