.ico
"ico" is a common extension for an icon. An icon is the image you see in a file browser or on your desktop. That icon will represent a file.
first make your icon in paint then save as an ordinary file (.jpg) then use the online tool , favico maker and upload your image. The online tool will make it an icon file then it gives you the option to download it
What is the file extension What is the file extension
There are good arguments both for and against disabling this option. If file extensions are not shown in explorer, renaming a file will not affect its extension. If an extension is accidentally removed, the file will not invoke the correct application and will not be useable until its extension is reinstated. If you cannot remember the correct file extension, you may not be able to reinstate the file. However, where you are trying to identify a file's extension, having them hidden can cause problems. The only indication of a file extension will be the icon displaying the application that it will be run under. Where you have several file types that run under the same application, it can be difficult to tell one from another without being able to see their file extensions.
file extension for video is 101
.html, .php, or .htm
The file extension tells about the type of file, with the extension three letters. For Eg:- *.txt -- text file *.exe-- executable file
file extension
the extension of a batch file is ".bat"
The file extension is ".pages"
The file extension of iPhone firmware file is .ipsw .
The extension .jpeg tells us the file is an image file