Microsoft is challenging Apple's filing for a trademark on the term "App Store," Good Gear Guide reports, because it feels the term is generic and that competitors should be able to use it as well.

In its 2008 filing with the U.S. Patent and Trademark Office, Apple defined an app store as "retail store services featuring computer software provided via the internet and other computer and electronic communication networks." Its App Store was launched that year, along with the iPhone 3GS. It now boasts more than 300,000 available apps. Most recently, Apple launched the Mac App Store just weeks ago, for use with its desktop computers and laptops. 

Microsoft filed a motion with the Trademark Trial and Appeal Board yesterday, challenging Apple's claim to the term. Apple's trademark request page says "an opposition is now pending."

Microsoft argues that both "app" and "store" are generic terms, and that consumers use the term "app store" generically to refer to an online store where applications are sold. It even used Steve Jobs' own words against him, quoting a published interview where the Apple CEO said, "Amazon, Verizon, and Vodafone have all announced that they are creating their own app stores for Android."

"Competitors should be free to use 'app store' to identify their own stores and the services offered in conjunction with those stores," Microsoft said.

Microsoft launched its own app store in conjunction with the release of Windows Phone 7 devices in October. By comparison, it had 4,000 available apps to download as of mid-December. Research firm IDC praised the quick ascent of the new OS's marketplace.