diff --git a/lib/matplotlib/colorbar.py b/lib/matplotlib/colorbar.py
index aac6179292ed..74634fb4c9a4 100644
--- a/lib/matplotlib/colorbar.py
+++ b/lib/matplotlib/colorbar.py
@@ -141,12 +141,17 @@
 Parameters
 ----------
 mappable
-    The `~matplotlib.cm.ScalarMappable` (i.e., `~matplotlib.image.Image`,
-    `~matplotlib.contour.ContourSet`, etc.) to which the colorbar applies.
+    The `matplotlib.cm.ScalarMappable` (i.e., `~matplotlib.image.Image`,
+    `~matplotlib.contour.ContourSet`, etc.) described by this colorbar.
     This argument is mandatory for the `.Figure.colorbar` method but optional
     for the `.pyplot.colorbar` function, which sets the default to the current
     image.
 
+    Note that one can create a `ScalarMappable` "on-the-fly" to generate
+    colorbars not attached to a previously drawn artist, e.g. ::
+
+        fig.colorbar(cm.ScalarMappable(norm=norm, cmap=cmap, ax=ax))
+
 cax : :class:`~matplotlib.axes.Axes` object, optional
     Axes into which the colorbar will be drawn.