gzip
gzip is a compression program
The gzip kioslave is not directly usable, and is intended for use as a filter. For example, the tar kioslave can filter a file through the gzip kioslave, in order to display the contents of a tar.gz file directly in a window.
If you click on a file compressed with a gz extension in , this kioslave is used to uncompress it and display it as a normal (uncompressed) file.
If you are a developer, and would like to use the gzip filter, you can find documentation on using kioslaves at http://developer.kde.org
See the manual: gzip.