Android is a software platform and operating system developed by google  for mobile devices.It is based on the Linux kernel. It allows developers to write managed code in the Java language, controlling the device via Google-developed Java libraries. Applications written in C and other languages can be compiled to ARM native code and run, but this development path is not officially supported by Google.
The unveiling of the Android platform on 5 November 2007 was announced with the founding of the Open Handset Alliance, a consortium of 48 hardware, software, and telecom companies devoted to advancing open standards for mobile devices.Google released most of the Android code under the Apache license, a free-software and open source license

You can find the detailed article in wikepedia here http://en.wikipedia.org/wiki/Google_android