There are plenty of places where users can download mobile apps these days, but there's only one App Store. Well, that's how Apple sees it at least.

Continuing on its quest to secure a trademark for "App Store", Apple last week filed suit against Amazon alleging that the online retailer was improperly using the phrase "App Store" in its mobile software developer program. Specifically, Apple accuses Amazon of trademark infringement and unfair competition. Apple of course is also currently engaged in a legal spat with Microsoft over the same issue. Microsoft, for what it's worth, isn't backing down and claims that the term "App Store" is too generic to warrant trademark protection.

As for Amazon, the complaint notes that Amazon began using the phrase in early 2011 and did not adequately respond to repeated Apple demands that they stop using the name. Indeed, the name of of the developer program is "Amazon AppStore" and the phrase is plastered throughout Amazon's pages detailing the program - which is geared towards enabling developers to sell their apps on Amazon.com.

Apple is concerned that other companies making use of the "App Store" moniker will ultimately confuse consumers and erode the brand cachet Apple has established with its own iTunes App Store which now houses over 400,000 apps and has seen over 10 billion downloads. Further, Apple rightfully views its own app store as a key differentiator between the iPhone and competitive offerings from the likes of Google and Microsoft. During Apple's recent iPad 2 unveiling, for example, Apple CEO Steve Jobs took a jab at Google's tablet experience by comparing the 65,000 native iPad apps available on the iTunes App Store against the minuscule number of apps available for Android tablets.

Now one might reasonably argue, as did Microsoft, that the term app store is a generic way to describe any mobile market where one might download applications. And while true, a phrase can be come so popular and so entrenched in the vernacular that it warrants a trademark. In a recent filing addressing Microsoft's opposition to Apple's app store trademark, Apple pointed out that Microsoft was able to secure a trademark for "Windows".

"Having itself faced a decades-long genericness challenge to its claimed Windows mark, Microsoft should be well aware that the focus in evaluating genericness is on the mark as a whole and requires a fact-intensive assessment of the primary significance of the term to a substantial majority of the relevant public," Apple's filing reads. "Yet, Microsoft, missing the forest for the trees, does not base its motion on a comprehensive evaluation of how the relevant public understands the term App Store as a whole."

So where does that leave us?

It's really hard to say.

From my experience, whenever someone refers to the iTunes App Store in conversation, they usually just say iTunes. Apple, though, maintains that the phrasing "app store" uniquely conjures up Apple in the mind of the public.

News of Apple's suit against Amazon was first relayed by Bloomberg. The actual court filing, however, is not yet available on PACER.