Webloc

Webloc is the Mac OS X version of what is done in Windows with the Internet Shortcut format, providing a link to a Web resource which can be put on your desktop.

The data fork of the file is empty, which makes the .webloc file seem like a completely empty file when viewed in non-Mac-specific utilities. The actual content is in the Resource Fork, which, in the case of a file stored as AppleDouble (as is usual for OS X filesystems) is in the file named with a dot and underscore prefixing the filename. This contains the linked URL.