Microsoft is no longer waging the battle against Apple's trademark of App Store just for itself, but is effectively representing all the companies that want to or are already trying to use the term "app store." Most recently, Amazon launched its own Android App Store and was promptly sued by Apple.

As such, Microsoft has filed yet another legal filing citing Amazon's new store as evidence that other companies need to be able to use the phrase to accurately describe their mobile application marketplaces. The issue is now in the hands of the US Trademark Trial and Appeal Board and will hopefully be resolved in the next few months.

Apple's bid for exclusive rights to the term is "at odds with the growing list of competitors using 'App Store' in their names and 'app store' to describe their stores, including the Amazon Appstore, launched March 22, 2011, by, Inc., the world's largest online retailer," Microsoft argues in the 13-page filing (PDF, courtesy of GeekWire). "These uses, despite Apple's continuing enforcement campaign, show beyond dispute that there is a competitive need for the term."

Microsoft's core argument is that "App Store" is as generic as "shoe store" or "toy store." As a result, the term should not belong to one company. The latest filing reiterates the software giant's position:

Apple strains to keep "App Store" for its exclusive use, even claiming that its online stores are not real stores, only metaphorical ones. But Apple cannot escape the hard truth: when people talk about competitors' stores, they call them "app stores." You don't have to look far to find this generic use – The Washington Post, The New York Times, The Wall Street Journal and even Apple's CEO Steve Jobs. And generic use of "app store" is not obscure or occasional as Apple would have us believe. It is prominent, ongoing and, by Apple's own measure, hundreds of times more frequent than the thin generic use in the cases upon which Apple relies.

Two months ago, Microsoft asked the US Patent and Trademark Office (USPTO) to reject Apple's application to trademark the term "App Store" because it is too generic. Earlier this month, Apple countered back by reminding Microsoft that it successfully trademarked "Windows" a few decades ago.

Putting away your opinion of Microsoft and Apple, which side of the argument are you on?