It's easy : chromium (http://www.chromium.org/) is the open source project. It's licence is open source and can be found at http://src.chromium.org/viewvc/chrome/trunk/src/LICENSE?revi... it looks like a "BSD with attribution" licence.
Chrome (google.com/chrome) is the "closed-source" distribution to loads of platforms (includes a few closed source components. E.g. it can play .mp3 files). It's got a standard closed source licence.
There are other distributions, for example "fedora" chromium, that doesn't have any codec support. There are versions that are not release-engineered (ie. nightly builds, but still released by some distro), ...