From: eLinux.org
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:
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
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
Also, go to Android Architecture on this site.