#2633: clarify meaning of env parameter.
diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index d1471f1..b93bd03 100644
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -93,8 +93,9 @@
searching the executable, so you can't specify the program's path relative to
*cwd*.
- If *env* is not ``None``, it defines the environment variables for the new
- process.
+ If *env* is not ``None``, it must be a mapping that defines the environment
+ variables for the new process; these are used instead of inheriting the current
+ process' environment, which is the default behavior.
If *universal_newlines* is :const:`True`, the file objects stdout and stderr are
opened as text files, but lines may be terminated by any of ``'\n'``, the Unix