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The definitions given by Google for Android
"Android is an open-source software stack for a wide range of mobile Devices and a corresponding open-source project led by Google."
"Android is an Operating system based on the Linux kernel with a user interface based on direct Manipulation, Designed primarily for mobile touchscreen Devices such as smartphones and tablet Computers[...]"
left me in doubt about the objectives of the platform.
Perhaps an answer that will explain the difference between OS and stack software will bring the reader the understanding about these two concepts.
I think that a particular section of the wiki answers your question.
– Oralista de Sistemas