What is a "desktop file"?

I am trying to create my first appimage and I have just read the online documentation. Most of it is clear, but there is one basic piece of information that I cannot find (overlooked?): how to create a desktop file and what its name or contents should be.

Google search for “appimage desktop file” does not seem to find this information either. Did I miss something? Is this something specific for appimage or is it a general thing for linux?

Desktop files are not specific to AppImage. Please see the freedesktop XDG desktop file specification.

You are right, thanks. I didn’t know desktop files and initially, I had some trouble finding the relevant documentation. This is the link that helped me: https://specifications.freedesktop.org/menu-spec/menu-spec-1.0.html