jargon.artrocity.com
New Hacker's Dictionary the Jargon File v 4.4.6
[very common; first heard c.1995] Short for ‘co-location’, used of a machine you own that is physically sited on the premises of an ISP in order to take advantage of the ISP's direct access to lots of network bandwidth. Often in the phrases co-lo box or co-lo machines. Co-lo boxes are typically web and FTP servers remote-administered by their owners, who may seldom or never visit the actual site.