Add extra note about free-threading.

Author: ZeroIntensity

Doc/glossary.rst

@@ -151,7 +151,8 @@ Glossary
       caller holds the :term:`GIL` for the current interpreter, so only
       one OS thread can have an attached thread state at a given moment. In
       :term:`free-threaded <free threading>` builds of Python, threads can concurrently
-      hold an attached thread state, allowing for true parallelism.
+      hold an attached thread state, allowing for true parallelism of the bytecode
+      interpreter.
 
    attribute
       A value associated with an object which is usually referenced by name