Peter Norvig

Lisp has special variables with dynamic scope. Dylan does not have this feature. However, Harlequin has provided an extension, fluid-  bind, that implements variables with dynamic scope.

/duim/utilities/stubs.dylan

The module duim-utilities contains the definition of the macro fluid- bind

Martin Gasbichler
and Michael Sperber

Quotes from their paper Processes vs. User-Level Threads in Scsh; ThirdWorkshop on Scheme and Functional Programming. October 3, 2002, Pittsburgh, Pennsylvania, USA.:

The dynamic environment contains thread-local bindings for fluid variables (or just fluids) that implement a form of dynamic binding local to a single thread.

A fluid is a cell that allows dynamic binding.

Fluids play a crucial role in coordinating thread-local state and process state.