If you ever wanted to create a new Environment Variable, you can do so by setting them in the VirtualHost section.
For example,

<VirtualHost *:80>
DocumentRoot /www/htdocs
ServerName www.my-dom.com
SetEnv VARNAME varValue
</VirtualHost>

And to use it in PHP simply use $_SERVER[‘VARNAME’] or getenv(‘VARNAME’);
If you were to check the output of phpinfo(), you can actually see the Environment Variable as the image illustrates below.