On September 2, 2016, Anna Chu, a community manager from the Office 365 Network at Microsoft, posted an announcement that the network is rebranding as the Microsoft Tech Community.
As Exchange MVP Tony Redmond pointed out in his article, Microsoft Launches New Office 365 Network Online Community; 88,000-User Yammer Network to Close in mid-July, a significant change to the Office 365 Network was announced, and Yammer as the main interface was likely to be deprecated in favor of a new platform that could be open to external search engines. It makes sense (to me) that the site would get a new name in order to make the break from the older Yammer-based network.
The current Office 365 Network will shut down September 15, 2016. As Anna indicated in her announcement, the URL of the new community will change soon to http://techcommunity.microsoft.com.
In making the change, Microsoft indicated that they are expanding the current Office 365 Network to integrate the Azure, Windows Server & SQL Server Communities and more communities in the future.