The acronym "VAM" is taken from the last name of the two people who studied and cataloged the die differences: Leroy Van Allen and A. George Mallis.
As a result of VAM studies, a wide assortment of varieties for the two series of coins have been discovered and catalogued.
Coin collectors were aware of Morgan dollar varieties and differences which were caused by dies.
A VAM occurs as a result of a die variety which creates the same variation on a number of coins.
Leroy Van Allen (VA) and A. George Mallis (M) documented the small variations and VAM comes from the initials of their last names.