There are two commonly accepted definitions of Augmented Reality today. One was given by Ronald Azuma in 1997. Azuma’s definition says that Augmented Reality

• combines real and virtual
• is interactive in real time
• is registered in 3D

Additionally Paul Milgram and Fumio Kishino defined Milgram’s Reality-Virtuality Continuum in 1994. They describe a continuum that spans from the real environment to a pure virtual environment. In between there are Augmented Reality (closer to the real environment) and Augmented Virtuality (is closer to the virtual environment).

More recently, the term augmented reality has been blurred a bit due to the increased interest of the general public in AR.

definition from Wikipedia

The first Augmented reality application for Iphone.

open source projects:

The Augmented Reality Tool Kit – ARToolKit captures images from video sources, optically tracks markers in the images, and composites them with computer-generated content using OpenGL. Dual-licensed, under the GPL, plus commercially by ARToolworks, Inc.

• download at: http://sourceforge.net/projects/artoolkit
• Flash AS3 ported version FLARToolkit is available here
• http://flash.tarotaro.org/blog/ – other Flartoolkit examples and other resources

more from the Web:

• http://layar.com – Layar is a free application available for the T-Mobile G1, HTC Magic and other Android phones which shows what is around you by displaying real time digital information on top of reality through the camera of your mobile phone.