The AppleScript dictionary of a scriptable application or a Scripting addition defines the terminology that a script must use to send commands to that software. Smile (and the other script editors) let you view the AppleScript dictionaries.
Thus the dictionary is a synthetic way of getting information about a scriptable software.

On this site you can view the dictionaries for all our software ...

• Dictionary of Smile
• Dictionary of Smile's Graphic Library
• Dictionary of Satimage.osax
• Dictionary of XMLLib.osax
• Dictionary of Numerics.osax
• Dictionary of FITS.osax
• Dictionary of SpecialFunctions.osax
• Dictionary of ConvexPoly.osax
• Dictionary of Geometry.osax