Proprietary means software (like an application or driver) that is not open-source. It is owned by a particular company or individual who is not willing to give out its source code, or does not allow the source to be used, changed, and redistributed. A common example of proprietary software in Ubuntu is the ATI Graphics Drivers.
Freeware is not open-source. Freeware refers to a program that is free of cost, but the source code is kept secret.
Microsoft Windows, Office, and other big name software such as Adobe Reader are proprietary software. Google Chrome is proprietary software, while Chromium is open-source.
Proprietary software is often referred to as closed-source. For more information, see http://en.wikipedia.org/wiki/Proprietary_software.