diff --git a/airflow-core/src/airflow/partition_mappers/temporal.py b/airflow-core/src/airflow/partition_mappers/temporal.py
index 1938a18f84da8..c16801c97b132 100644
--- a/airflow-core/src/airflow/partition_mappers/temporal.py
+++ b/airflow-core/src/airflow/partition_mappers/temporal.py
@@ -469,9 +469,11 @@ class FanOutMapper(PartitionMapper):
     is N→1 (downstream waits until all members arrive), fan-out is 1→N (one
     upstream event creates one downstream Dag run per member).
 
-    For forward fan-out (emit the trailing period ending at the upstream key,
-    instead of the period it represents), pass ``direction=Window.Direction.FORWARD``
-    to the window:
+    ``window``'s direction controls which period each upstream key fans out to.
+    The default, ``Window.Direction.FORWARD``, yields the period *starting at*
+    the upstream key (the period it represents); ``Window.Direction.BACKWARD``
+    yields the trailing period *ending at* the upstream key. Pass
+    ``direction=Window.Direction.BACKWARD`` to the window for the latter:
 
     .. code-block:: python
 
@@ -482,8 +484,8 @@ class FanOutMapper(PartitionMapper):
         FanOutMapper(upstream_mapper=StartOfWeekMapper(), window=WeekWindow())
 
         # Weekly upstream → the 7 days ending at the upstream Monday (trailing period)
-        forward_window = WeekWindow(direction=Window.Direction.FORWARD)
-        FanOutMapper(upstream_mapper=StartOfWeekMapper(), window=forward_window)
+        backward_window = WeekWindow(direction=Window.Direction.BACKWARD)
+        FanOutMapper(upstream_mapper=StartOfWeekMapper(), window=backward_window)
     """
 
     # Keep ``FanOutMapper.default_downstream_mapper_by_window_name`` in sync with
diff --git a/task-sdk/src/airflow/sdk/definitions/partition_mappers/temporal.py b/task-sdk/src/airflow/sdk/definitions/partition_mappers/temporal.py
index 0cf0a705d5cdd..ccb1497f0325b 100644
--- a/task-sdk/src/airflow/sdk/definitions/partition_mappers/temporal.py
+++ b/task-sdk/src/airflow/sdk/definitions/partition_mappers/temporal.py
@@ -137,20 +137,23 @@ class (e.g. ``WeekWindow`` → ``StartOfDayMapper``).
     waits for all members), fan-out is 1→N (one upstream event creates many
     downstream Dag runs).
 
-    For forward fan-out (emit the *next* period's members instead of the current
-    one), pass ``direction=Window.Direction.FORWARD`` to the window:
+    ``window``'s direction controls which period each upstream key fans out to.
+    The default, ``Window.Direction.FORWARD``, yields the period *starting at*
+    the upstream key (the period it represents); ``Window.Direction.BACKWARD``
+    yields the trailing period *ending at* the upstream key. Pass
+    ``direction=Window.Direction.BACKWARD`` to the window for the latter:
 
     .. code-block:: python
 
         from airflow.sdk import WeekWindow, Window
         from airflow.sdk.definitions.partition_mappers.temporal import FanOutMapper, StartOfWeekMapper
 
-        # Weekly upstream → 7 daily downstream Dag runs (current week)
+        # Weekly upstream → 7 daily downstream Dag runs (the 7 days the upstream Monday represents)
         FanOutMapper(upstream_mapper=StartOfWeekMapper(), window=WeekWindow())
 
-        # Weekly upstream → 7 daily keys for the *following* week
-        forward_window = WeekWindow(direction=Window.Direction.FORWARD)
-        FanOutMapper(upstream_mapper=StartOfWeekMapper(), window=forward_window)
+        # Weekly upstream → the 7 days ending at the upstream Monday (trailing period)
+        backward_window = WeekWindow(direction=Window.Direction.BACKWARD)
+        FanOutMapper(upstream_mapper=StartOfWeekMapper(), window=backward_window)
     """
 
     # Keep ``FanOutMapper.default_downstream_mapper_by_window_name`` in sync with