Without having more information, let me see if I can answer the question.
First, ASH stands for Advanced Script Handling. Damn... I forget the name of the guy behind it. Apologies to you, if you ever read this.
But basically it came about as more and more people started running into the brick walls that were the limitations in the standard scripting language that mafia uses.
So, instead of forcing everyone to use a more advanced language, or the simpler - but feature light - standard language, whoever it was behind it presented the ASH language "module" for mafia. (I am not entirely sure how it was incorporated. Module is just a term I am using.)
Mafia can run either type of script, with the provision that an ASH script must have an extension of ".ash".