Android is an operating system, originally made for cell phones, but is also available for tablets. Android has also been ported to run on desktop computers as well. http://www.android-x86.org/
Android has recently taken the mobile phone market by storm. As of September 7th 2010, Android holds 16.3% of the smartphone market, as compared to the iPhone's iOS 14.7%. Android is one of the most rapidly growing smartphone platforms available right now, and is projected to hold 51.2% of the smartphone market by 2014.
Dan Morrill explained in On Android Compatibility, “Android is not a specification, or a distribution in the traditional Linux sense. It’s not a collection of replaceable components. Android is a chunk of software that you port to a device.”
Linux · Underneath everything is a reasonably up-to-date Linux Kernel. Android runs on Linux, but but it isn't exactly a distro because it leaves out so much that people expect in one: libraries and shells and editors and GUIs and programming frameworks. It’s a pretty naked kernel, which becomes obvious the first time you find yourself using a shell on an Android device.
Dalvik · The next big piece of Android is Dalvik, comprising the VM and a whole bunch of basic runtime essentials. All the standard APIs that you use to create Android apps are defined in terms of Dalvik classes and interfaces and objects and methods.
How It’s Generated · Native code is currently produced more or less exclusively by compiling C or C++ code; but that isn't the only way you can code for Android. Dalvik code is currently produced by generating Java bytecodes and translating them, but again, there are many ways you can program apps for Android.
Android apps are defined as code that runs on the platform and uses the APIs. As long as an app does these things properly, it doesn't matter how it got generated.
What’s In an App? · An Android app lives in what’s called an APK file, basically a ZIP file with a particular internal file layout that allows it to be run in place, without unpacking. There’s nothing magic about them, you can email them around and drop them on USB drives and extract pieces by unzipping.
Android is an amazing operating system, but there is much more to it than all this technical mumbo-jumbo. The part of Android that i believe everybody should look into because it personifies open source nature of Android, is rooting. More on rooting in my next article.