The term "synergy" is a horribly over-used cliche in the tech world these days. Everyone loves to use it to describe the way in which one group, or product, or idea can spark grwoth in other areas and foster a larger ecosystem.

In the case of the App Store, however, it's a pretty valid label. On Monday Apple announced that the iPhone/iPod Touch App Store service had served up its two-billionth download. This comes just five months after hitting the one billion download mark and a little more than one year after the first Apps went on sale.

This amazing growth comes as the latest example of what has become a digital media powerhouse stemming from the iPod and iTunes.

How rapidly is the service growing? Well, in 2003 the iTunes store first began selling music online. Shortly after, sales for the iPod and iPod nano took off in full force. With more users on iTunes, the store sold more songs, and people became familiar with the iTunes environment.

Then in 2007 we get the iPhone, which is aided not only by its own hype, but also by the idea that it carried on much of the iPod's design and usability. Then 2008 rolls around and Apple opens up the App Store. Now, not only is there a massive user base from iPhone and iPod Touch users, but you also have customers accessing the store to purchase music and then finding that they can also buy apps on a similar interface.

In that way, one can virtually trace the 2 billionth App sale back to 2003 and the launch of the iPod. Quite an interesting evolution.