A mash bill is a document that specifies the proportions of different grains used to make whiskey. “Mash bill #2” is not a specific term in the whiskey industry, but it can be used to refer to a particular whiskey recipe or the second mash bill used by a particular distillery.
The specific grains and proportions used in a mash bill can have a significant impact on the flavor of the resulting whiskey. For example, a mash bill that uses a high proportion of corn will produce a whiskey with a sweeter flavor, while a mash bill that uses a high proportion of rye will produce a whiskey with a spicier flavor. The type of yeast used can also affect the flavor of the whiskey.