The application class is used mainly to specify a target. This, in effect, is the primary act of AppleScript programming. You specify a target so that you can send messages to it, and sending messages to an application is the purpose of AppleScript.
You specify an application using an object string specifier the word application followed by a string representing the application's name or (colon-delimited) pathname. An abbreviation for application is app. For further details on how to target an application using an application specifier, see "Local Applications" in Chapter 23.