Glad to see you back, hftvol. Colocation in general means leasing rack space, bandwidth and power in a datacenter, regardless if your server runs a game server, an email server or a dating site. Several years into the colocation era, exchanges figured out a way to make some extra money, other than crossing orders and selling data. Allow servers to be placed within the same datacenter they run their engines. Banks & hedge funds jumped into it and they colocated into the same datacenters as the exchanges. If you never bothered reading about hosting email severs, game servers or dating sites, but instead you only read about HFT you would think the term 'colocation' means placing a server in an exchange datacenter and come up with a new term 'proximity hosting' for everything else. To put it in another way, if someone hosts an adult web site on any datacenter, that datacenter will bill for 'colocation' and not for 'proximity hosting'. Talking about trading and server hosting in the same sentence does not invalidate any of the standard IT terminology and there is no need to come up with new terminology.