In Common Lisp let is either lexically or dynamically scoped, depending on whether the symbol is marked "special" which is the situation if the symbol was previously used as the name in a defvar or defparameter form to define a dynamic variable.

So dynamically scoped contexts are achieved just by binding these special variables. By convention, they are usually given names beginning and ending with an asterisk ("earmuffs") to put them into an effectively separate namespace.

That parametrize is reminiscent of fluid-let; another Scheme hack to simulate dynamic scope.