Avoid talking about how threads are scheduled.

Author: ericsnowcurrently

Doc/reference/executionmodel.rst

@@ -414,18 +414,22 @@ on the computer look something like this::
 Hosts and processes are isolated and independent from one another.
 However, threads are not.
 
-While a program always starts with exactly one thread, known as the
-"main" thread, it may grow to run in multiple.  Not all platforms
-support threads, but most do.  For those that do, each thread does *run*
-independently, for the small segments of time it is scheduled to execute
-its code on the CPU.  Otherwise, all threads in a process share all the
-process' resources, including memory.
+A program always starts with exactly one thread, known as the "main"
+thread, it may grow to run in multiple.  Not all platforms support
+threads, but most do.  For those that do, all threads in a process
+share all the process' resources, including memory.
+
+Each thread does *run* independently, at the same time as the others.
+That may be only conceptually at the same time ("concurrently") or
+physically ("in parallel").  Either way, the threads run at a
+non-synchronized rate, which means global state isn't guaranteed
+to stay consistent for any given thread.
 
 .. note::
 
    The way they share resources is exactly what can make threads a pain:
-   two threads running at the same arbitrary time on different CPU cores
-   can accidentally interfere with each other's use of some shared data.
+   two threads running at the same time can accidentally interfere with
+   each other's use of some shared data.
 
 The same layers apply to each Python program, with some extra layers
 specific to Python::