Clarify docs to explain that max_fail_percentage uses batch size (#33720)

docs/docsite/rst/playbooks_delegation.rst

@@ -80,9 +80,9 @@ You can also mix and match the values::
 Maximum Failure Percentage
 ``````````````````````````
 
-By default, Ansible will continue executing actions as long as there are hosts in the group that have not yet failed.
+By default, Ansible will continue executing actions as long as there are hosts in the batch that have not yet failed. The batch size for a play is all the hosts specified in the ``hosts:`` field.
 In some situations, such as with the rolling updates described above, it may be desirable to abort the play when a
-certain threshold of failures have been reached. To achieve this, as of version 1.3 you can set a maximum failure 
+certain threshold of failures have been reached. To achieve this, you can set a maximum failure
 percentage on a play as follows::
 
     - hosts: webservers