As you may recall Windows & Windows Phone 8.1 was codenamed “Blue.” The codename for the next set of major updates for Windows, Windows Phone, and Xbox will be ‘Threshold.’ MJF reports:
Microsoft Executive Vice President Terry Myerson recently mentioned the Threshold codename in an internal email about plans for his unified operating-system engineering group.
The goal of threshold will be to develop the next version of each respective OS in a way that shares more common elements and support a core set of “high value activities”. Full unification may comes after Threshold. Terry Myerson is currently in charge of the road map until the new CEO comes in, and the plan is to release the Threshold wave of products in Spring of 2015. In the meantime the Windows team is working on releasing “Update 1″ in Q2 of 2014, shortly after the release of Windows Phone 8.1.
Threshold is believed to be a reference to a planet in Halo, similar to another codename, Cortana, that is also referenced from Halo. Threshold was also a popular science fiction TV series.
Source: Mary Jo Foley