Windows Mobile was a Micrososft operating system that targeted smartphones and Pocket PCs. It was first released in the Pocket PC 2000 operating system and was based on the Windows CE kernel. Windows Mobile included basic applications developed with the Microsoft Windows API and options for customization and software development with no restrictions by Microsoft. Applications for the software were available for purchase from Windows Marketplace for Mobile.
In 2010, Microsoft announced the development of Windows Phone to supercede Windows Mobile.
Techopedia explains Windows Mobile
Windows Mobile supplied a basic suite of applications that was designed to be similar to the desktop version of Windows. It also came bundled with a set of applications, including Internet Explorer Mobile, Windows Media Player and Microsoft Office Mobile. Initially, Windows Mobile devices required a stylus. They later evolved toward capacitive touch screens.
Devices designed to run Windows Mobile cannot run software for the newer Windows Phone because they lack the hardware requirements for this higher powered software.