Office 2007 Service Desk Edition

Hello guys n gals
I tried to buy a MS office 2007 Home and Student Edition for a client from my usual software supplier but they were out of stock.
I needed it quickly so I bought a retail version from Amazon.
It arrived today and it has “Service Desk Edition” printed on the case label.
Being the brainless know-nothing numpty that I am I have no idea what this means or what the difference is from any other edition.
Can anyone explain?
Come on Smeg, Box, Mr Mycroft, etc I know the answer is out there