Android is a Linux-based operating system for mobile devices such as smartphones and tablet computers, developed by Google in conjunction with the Open Handset Alliance. The first Android-powered phone was sold in October 2008, and by the end of 2010 Android had become the world's leading smartphone platform. It had a worldwide smartphone market share of 59% at the beginning of 2012, and as of third quarter 2012, there were 500 million devices activated and 1.3 million activations per day.
Android was initially developed by Android Inc, whom Google financially backed and later purchased in 2005. The unveiling of the Android distribution in 2007 was announced with the founding of the Open Handset Alliance, a consortium of 86 hardware, software, and telecommunication companies devoted to advancing open standards for mobile devices.
Google releases the Android code as open-source, under the Apache License. The Android Open Source Project (AOSP) is tasked with the maintenance and further development of Android. Additionally, Android has a large community of developers writing applications ("apps") that extend the functionality of devices. Developers write primarily in a customized version of Java, and apps can be downloaded from online stores such as Google Play (formerly Android Market), the app store run by Google, or third-party sites. In June 2012, there were more than 600,000 apps available for Android, and the estimated number of applications downloaded from Google Play was 20 billion.
Source: Wikipedia - http://en.wikipedia.org/wiki/Android_(operating_system)