ActionScript 3 Tutorial
ActionScript 3 is the programming language for the Adobe Flash Player and Adobe AIR runtime environments. It is object-oriented ECMAScript based language used primary for native application development on desktop (Windows/Mac) and mobile (iOS/Android) devices.
Adobe learning resources: http://www.adobe.com/devnet/actionscript/learning.html
History and more details: https://en.wikipedia.org/wiki/ActionScript
Online documentation on classes and reference: http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/package-detail.html