This article shows how to define other environment variables in addition to the predefined ones.
Menu path: System > System Customization > Environment Variables > Additional
To manage the list of Additional variables:
Click
to create a new entry.Click
to remove the selected entry.Click
to edit the selected entry.Click
to copy the selected entry.
Clicking 
brings up the Add dialogue, where you can define the following settings:
Variable name
Name for the variable
Value
Value for the variable