_wordpress-cache in server name

[Ian M. Evans]

I saw this example for setting up nginx to run wordpress and wp-super cache

server_name _wordpress-cache mydomain.com;
root /var/www/wordpress_dir;
server_name_in_redirect off;

Can anyone explain to me what the "_wordpress-cache" is doing in the
server name area. Guess I'm trying to wrap my head around new config
options.

Thanks!