This option contains the name your client will identify itself under to other peers.
In most cases, your client_name doesn't matter, and you can leave it at default value, or use it as a vanity plate. However, a few eDonkey/eMule clients can be configured to prefer clients with certain tags in their names, thus forming some kind of communities. Similarily, a little number of servers will only accept clients that have specific tags in their IDs, too.
By default, client_name is set to some random string.
This option is stored in downloads.ini
> set cliet_name MyCyberDonkeyRulez