What does locked to US Cellular mean?

We're buying an iphone 5c off of eBay and we read the description and it says it's locked to us cellular what does that mean?

That it could only work on that network, though (un)locked phones usually only apply for GSM phones on GSM networks, US Cellular being a CDMA one

It will not be usable where US Cellular doesn't provide service.

US Cellular uses its own network in its "home" territory, and has roaming agreements with Verizon elsewhere. Thus the devices use Verizon's CDMA technology.

If the phone is unlocked, it can be used on those networks. If not already unlocked, US Cellular has a fairly liberal unlocking policy (see link).

Personally, I would prefer a GSM (AT&T or T-Mobile) phone, because the GSM technology is used in more places globally than CDMA, and switching phones/numbers etc is much easier by merely swapping SIM's.

Still, Verizon's coverage is excellent, and their Customer Service gets good reviews, and their network is also available using Walmart' s StraightTalk system. (Straight Talk is also available for AT&T, T-Mobile and Sprint phones)