Company ve corporation anlamına geliyor. 20+ ülkede .co.uk , co.jp gibi şirketlerin aldığı uzantılar arasında. Tabi colombia, colorado gibi yer uzantısını da çağrıştırıyor. Gördüğüm kadarıyla ing. alan adlarında bu uzantı değerli.

Ayrıntılı bilgi:

"It's the acronym for "company". For most people1, the two letters – CO – are recognized as meaning company and/or corporation across the globe. Look around and someone near you is already using the letters CO in that context.
It's used in country-code domain extensions. More than 20 countries use .CO to mean company and/or commercial content in their websites (e.g. .co.uk, .co.in, .co.il, .co.jp, etc.). By adding a .CO domain to their online marketing strategy, country specific websites can now have a version of their site serving their global customers.
In other uses it has geographic meaning. CO means Colombia and it also means the State of Colorado in the USA."