Short for Co-located, where you own a computer, send it to a service company, and they install it in their racks. You own the computer box, they plug it into fast internet connections, uninterruptible power supplies with generator backup, and possibly behind firewall hardware. Some will sell you a computer from their inventory as well, new and/or used.
Same as above but you rent their computer rather than provide your own. With today's low costs for computing hardware, this may not make financial sense.
- Virtual Server
You pay rent for a certain speed and number of processor cores, certain amount of disk space, and bandwidth and/or traffic. But it's all imaginary. You don't actually control a specific computer box, processor, or hard drive. Your virtual server is one of many others operating across a server farm, large arrays of computers. Some services let you shut down your virtual server but store your disk space while reducing the bulk of your cost. This is handy for test machines, or trial runs before launching your full-time servers.
In the first two categories, my professional contacts, previous research, and word-of-mouth leads me suggest the following companies to someone looking for a vendor:
Do your own research and shopping, but those vendors may be a good place to start.