A lot of people used to just say "encrypted" which led people to believe the only possible way to view cablecard content at all was WMC. There was a time when your cable subscription would come with unencrypted QAM channels available on the coax outlets in your house, so each TV could get "something" even though it was usually just locals. The boxes that you lease from a cable company have a cablecard decrypter built-in and the cablecard is tied to your account so you only "get what you pay for"
Then WMC came along from Microsoft and created a DRM schema called "PlayReady" and enabled it within the wtv file format created by WMC. All of this prior to the consumer release of a cablecard tuner mind you
and then provided an "extender" model where devices like the xbox 360 and other licensed "extenders" could share those recordings because their video playback chain supports the DRM mechanism they created and don't allow you to tap into it and copy all of your HBO shows (which was kind of the point of cablecard encryption to begin with)
Within that DRM mechanism they honor a short bit of metadata built into the encrypted QAM stream called "Copy Control Information" or CCI. The CCI bit we refer to when we say "Copy Once" is 0x1. That means any approved DVR software (of which there is only one, WMC) can record and playback that stream. Those recordings can be copied around as much as you want, but they will not playback anywhere other than the WMC machine you recorded them on (or an extender that is tied to that instance of WMC). If you brick that machine's OS drive and re-install, those recordings will no longer play back (except within a few extreme scenarios where you do some full bare metal re-install and know more than I do about what other gotchas exist in that scenario)
There are cable companies that mark every channel Copy-Once (even Local SD and Local HD) like TWC
There are cable companies that mark only a few channels Copy-Once from their standard fare ~ like Verizon and Comcast
All cable companies mark HBO, Cinemax, Starz, and Encore copy-once
There are also bits like 0x2 which is Copy-Never. This applies to PPV, to prevent any copy from being made
The one we are looking for when we want to "run our own" version of Microsoft's extender model via ServerWMC is 0x00 (Copy-Freely). It may seem surprising, but all channels on Verizon FiOS used to be copy-free. For about 3 years now, every cableco including verizon enforces copy-once on their premium subscription channels HBO, etc. As stated, there are still a lot of Comcast and Verizon channels marked Copy-Free. In my experience with the lowest tier Comcast Digital Cable TV (not digital economy, but the one with ESPN and 40+HD channels) I only encountered copy-once on Sprout, National Geographic, intermittent Palladia, and DisneyXD
Fortunately most people have stopped simply referring to "encrypted" cable, since all QAM cable in the USA is now encrypted. The output of the cablecard tuners like the HDHR Prime and Ceton is decrypted (via cablecard) but will only play nicely outside of WMC if it is not "copy-once"