In the terminology of Dreamweaver behaviors, an action is what happens when an event occurs.
Thus, Open Browser Window is an action, Swap Image is an action, etc.
(In practice, people tend to say “behavior” rather than “action”.)
Dreamweaver behaviors have changed somewhat from version to version; you may encounter compatibility issues, if you work spans two or more versions of Dreamweaver.
Additional behaviors are available from third-party sources.
You can write your own custom behaviors using JavaScript.
Dreamweaver CS5 and CS5.5 have these built-in actions:
- Apply the Call JavaScript behavior
- Apply the Change Property behavior
- Apply the Check Browser behavior
- Apply the Check Plugin behavior
- Apply the Control Shockwave or SWF behavior
- Apply the Drag AP Element behavior
- Gathering information about the draggable AP element
- Apply the Go To URL behavior
- Apply the Jump Menu behavior
- Apply the Jump Menu Go behavior
- Apply the Open Browser Window behavior
- Apply the Play Sound behavior
- Apply the Popup Message behavior
- Apply the Preload Images behavior
- Apply the Set Nav Bar Image behavior
- Apply the Set Text Of Frame behavior
- Apply the Set Text Of Container behavior
- Apply the Set Text Of Status Bar behavior
- Apply the Set Text Of Text Field behavior
- Apply the Show-Hide Elements behavior
- Apply the Show Pop-Up Menu behavior
- Add, remove, and rearrange pop‑up menu items
- Format a pop‑up menu
- Position a pop‑up menu in a document
- Modify a pop‑up menu
- Apply the Swap Image behavior
- Apply the Validate Form behavior
Source:
http://help.adobe.com/en_US/dreamweaver/cs/using/WSc78c5058ca073340dcda9110b1f693f21-7b14a.html
