ActionScript is Adobe's scripting language for Flash. There are huge differences between different versions. See the Actionscript Wikipedia article for a timeline.
The latest version of ActionScript - ActionScript 3 since 2006 and Flashplayer 9 - is a scripting language based on ECMAScript 4.
See in this Wiki (and then follow up other entries)
- Flash ActionScript 3 overview for a general introduction.
- Actionscript 3 for AS3 related programming tutorials
- Flash - entry page about Flash (and Flash tutorials)
If you are looking for nothing but links: