Add note on what "variadic" is and pop into index

Author: zoffixznet

doc/Type/Signature.pod6

@@ -266,8 +266,10 @@ be omitted.
 
 =head2 X<Slurpy (A.K.A. Variadic) Parameters|parameter,*@;parameter,*%,slurpy argument (Signature)>
 
-An array or hash parameter can be marked as I<slurpy> by leading asterisk(s),
-which means it can bind to an arbitrary amount of arguments (zero or more).
+A function is X<variadic> if it can take a varying number of arguments; that is, its arity is not
+fixed. Therefore, optional, named, and slurpy parameters are variadic. An array or hash parameter
+can be marked as I<slurpy> by leading asterisk(s), which means it can bind to an arbitrary amount
+of arguments (zero or more).
 
 These are called "slurpy" because they slurp up any remaining arguments
 to a function, like someone slurping up noodles.