A VariableList is a link type used to declare a list of variables. It can be used to define a signature for a LambdaLink or a BindLink. A variable list consists entirely of a set of variable and variable type declarations, and nothing more.
VariableList VariableNode "$A" VariableNode "$B"
declares an argument list consisting of two arguments. A more complex example, consisting of type declarations for the variables, would be:
VariableList TypedVariableLink VariableNode "$F" TypeNode "ConceptNode" TypedVariableLink VariableNode "$C" TypeNode "ConceptNode"
declares a signature where both arguments must be ConceptNodes.