AppleScript: The Definitive Guide, 2nd Edition

Script

The word "script," like a number of terms associated with AppleScript, is liable to be tossed rather loosely about in a bewildering variety of senses. Some of its meanings are technically important and therefore indispensable, so it will help if we pause to clarify its chief uses explicitly.

Script as Drive

To "script" an application is to automate it, to drive it, to target it. People say, "I'd like to script the Finder to rename some files automatically." There is an implication that the Finder already has the power to do things to files, and that we are merely taking advantage of this power by dictating programmatically a sequence of actions that the Finder should take. This, after all, is why the Finder is said to be "scriptable" in the first place.

This sense of "script" is formalized in the way some sources define a "scripting language." This quotation comes from the ECMAScript Language Specification (http://www.ecma-international.org/publications/standards/ECMA-262.htm):

A scripting language is a programming language that is used to manipulate, customise, and automate the facilities of an existing system. In such systems, useful functionality is already available through a user interface, and the scripting language is a mechanism for exposing that functionality to program control. In this way, the existing system is said to provide a host environment of objects and facilities, which completes the capabilities of the scripting language.

That is a perfect description of AppleScript. ...