WinMo, which is short for Windows Mobile, is an operating system created by Microsoft for devices like mobile phones and PDAs. The latest version of WinMo is 6.5, with later versions of the operating system taking on the name Windows Phone.
Windows Mobile has since been rebranded as Windows Phone Classic, in keeping with the new naming convention.
The popularity of WinMo has been waning in the face of competition from iPhone, Android and Blackberry, although Windows Phone 7 does address a lot of the limitations in WinMo. Microsoft has stated that WinMo based devices can not be upgraded to Windows Phone 7.