Definition - What does Windows Mango mean?
Windows Mango is the the codename for the Windows Phone 7.5 OS. With Mango, Microsoft has claimed there are over 500 improvements from Windwos Phone 7, specifically a new "conversation view," faster browsing via Internet Explorer 9, and other features that will bring Windows phones up to speed with Android and iOS.
Techopedia explains Windows Mango
In late July 2011, Mango was revealed in Tokyo with consumers in that area being able to purchase a Mango-based phone in September of the same year. Mango is the first in a series of Windows Phones OS handsets to be released over the course of 2 years.
Windows phones through this version have not yet achieved widespread popularity, despite some decent reviews.