What is android?

Android is a software stack for mobile devices that includes an operating system, middleware and key applications.
Android SDK provides tools for developing android applications using Java programming language. 

Features of android OS

•        Application framework enabling reuse and replacement of components
•          Dalvik virtual machine optimized for mobile devices 
•          Integrated browser based on the open source WebKit engine
•          Optimized graphics powered by a custom 2D graphics library; 3D graphics based on the OpenGL  ES 1.0 specification (hardware acceleration optional)
•          SQLite for structured data storage
•          Media support for common audio, video, and still image formats (MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF)
•          GSM Telephony (hardware dependent)
•          Bluetooth, EDGE, 3G, and WiFi (hardware dependent)
•          Camera, GPS, compass, and accelerometer (hardware dependent)
•          Rich development environment including a device emulator, tools for debugging, memory and performance profiling, and a plugin for the Eclipse IDE

Android architecture 

 

credits:http://developer.android.com/guide/basics/what-is-android.html