According to several reports, the name was ditched after Metro AG, a Dusseldorf, Germany-based conglomerate that's the world's fifth-largest retailer, complained.

Microsoft and Metro AG both declined to comment on the origin of the name change.

Also last week, websites such as The Verge and bloggers like ZDNet's Mary Jo Foley said their sources had said Microsoft was telling developers, partners and employees that by such phrases as "Windows 8 design" and "Modern UI."

As of Wednesday, there were still four free apps in the Windows Store that used the word "metro" in their titles, including and "Tweet Paint Metro."

It's unclear whether those apps' names will have to be changed, or if they will be "grandfathered" in under earlier rules.