Plurality is a Function Parameter.
If it was not then you would not be able to close the edit custom function dialog box.
What plurality means in the context of the file is all dependent on the layout naming convention.
In your example Plurality = 2....
this returns @Table
If plurality was set to 1...
TableName (1) then the function returns the layout name with the last character removed.
This suggests that the layout naming convention can have pluralization.
i.e. layoutName or layoutNames