Android is a software platform and operating system written by Google and the Open Handset Alliance, designed for use in small form factor devices and smartphones.
The Android wikipedia entry is a really good place to get an overview of Android capabilities, history and direction. I won't duplicate the information from that site here.
The official web site for Android is http://www.android.com/. From here you can find links to:
- Android Market - This is the place where developers can post (for free or for sale) applications to run on Android-based devices, and where users can download these applications.
- Android Developer Site - Where software developers can learn how to write applications for Android devices, or modify aspects of the Android software itself.
- Android Open Source Project - This is where you can find the source code for the Android operating system (including Linux kernel, the libraries, Dalvik VM and rest of the Android system.)
Clicking on the "What is Android" tab takes you to: http://www.android.com/about/, which has some high-level bullet points, and a video with a little bit of Android history.
In November, 2007, Google released a video showing some of the features of their early prototype work on Android. See http://www.youtube.com/watch?v=1FJHYqE0RDg
G1 Product Video
The first phone product based on Android was the G1, manufactured by HTC and shipped by T-Mobile.
The G1 home page is at: http://www.t-mobileg1.com/. This site contains many videos and voiceovers describing G1 and Android features.
Engadget Hand's-on walkthrough of G1 features (September, 2008) http://www.engadget.com/2008/09/23/video-android-walkthrough-on-t-mobile-g1/
A good place to start, for technical information, is Google's "What is Android?" page
Another good place with technical information is Android FAQ