What is Android?

1.Android in Common and on Wiki:

Android in Common: 

There's no other software quite like Android. Google engineered Android, and Google’s own apps run best on it. And with millions of apps, games, songs, and videos on Google Play, Android is great for fun, and for getting things done.

Android devices come in all kinds of sizes, with all sorts of features, and at all sorts of prices. Each version of Android is named after a dessert, and the most recent version of Android is Jelly Bean and upcoming is KitKat. With Android, you’re in control of your mobile experience. 

definition from android.com

Android on Wiki:

Android is a Linux-based operating system designed primarily for touchscreen mobile devices such as smartphones and tablet computers. Initially developed by Android, Inc., which Google backed financially and later bought in 2005, Android was unveiled in 2007 along with the founding of the Open Handset Alliance: a consortium of hardware, software, and telecommunication companies devoted to advancing open standards for mobile devices. The first Android-powered phone was sold in October 2008.

Android is open source and Google releases the code under the Apache License. This open-source code and permissive licensing allows the software to be freely modified and distributed by device manufacturers, wireless carriers and enthusiast developers. Additionally, Android has a large community of developers writing applications ("apps") that extend the functionality of devices, written primarily in a customized version of the Java programming language.

2.What is Android?

Defination:

Android is an operating system based on the Linux Operating System.The project responsible for developing the Android system is called the Android Open Source Project (AOSP) and is primarily lead by Google.

Android For Newbies:

The Android development enviroment.An integrated set of tools to help you create your own Android applications.Android platform is a software stack for building and running mobile applications.And if you've used an Android device, to write email, to take photos, to get directions, to play games and so on, then you've seen the Android platform in action.And you have a good idea about what it can do.

Android System Supports:

   it supports background processing, provides a rich user interface library, supports 2-D and 3-D graphics using the OpenGL libraries, access to the file system and provides an embedded SQLite database.also Android applications consist of different components and can reuse components of other applications. 

  

Android Platform Components:

The Android system is a full software stack which is typically defined into the following four areas.

• Applications - The Android Open Source project contains several default application, like Home,Contacts,Phone,Browser, Camera, Gallery, Music, Phone and more.
  
• Application framework - API which allow for high-level interaction with the Android system from Android applications,like Activity Manager,Window Manager,Content Providers and more.
  
• Libraries and runtime - Libraries for the Application Framework for many functions (graphic rendering, data storage, web browsing, etc.) contains Surface Manager, Media FrameWork, SQlite etc and the Dalvik runtime and the core Java libraries for running Android applications.
  
• Linux kernel - Communication layer for the underlying hardware.contains Driver Display, Camera Drive, Flash Memory Driver etc.
  

This architecture is depicted in the following graphic.

 Task:

A task is a collection of activities that users interact with when performing a certain job. The activities are arranged in a stack (the "back stack"), in the order in which each activity is opened.

The device Home screen is the starting place for most tasks. When the user touches an icon in the application launcher (or a shortcut on the Home screen), that application's task comes to the foreground. If no task exists for the application (the application has not been used recently), then a new task is created and the "main" activity for that application opens as the root activity in the stack.

or 

The reuse of components of other applications leads to the concept of a task in Android; an application can reuse other Android components to archive a task. For example you can trigger from your application another application which has itself registered with the Android system to handle photos. In this other application you select a photo and return to your application to use the selected photo. 

Google Play:

Google offers the Google Play service in which programmers can offer their Android applications to Android users. End users use the Google Play application which allows to buy and install applications from the Google Play service.

Google Play also offers an update service. If a programmer uploads a new version of his application to Google Play, this service notifies existing users that an update is available and allows them to install the update.

Google Play provides also access to services and libraries for Android application programmers. For example it provides a service to use and display Google Maps and another to synchronize application state between different Android installations. Providing these services via Google Play has the advantage that they are available for older Android releases and can be updated by Google without the need for an update of the Android release on the phone.