diff --git a/lectures/4_segmentation.ipynb b/lectures/4_segmentation.ipynb
index c82353b..cda3a0f 100644
--- a/lectures/4_segmentation.ipynb
+++ b/lectures/4_segmentation.ipynb
@@ -246,7 +246,7 @@
    "source": [
     "## Examining the resulting segmentation\n",
     "\n",
-    "That's pretty good! Some coins are perfectly segmented, with only one missing. We can't do much about the missing one (yet), but we can [*merge regions*](http://scikit-image.org/docs/dev/auto_examples/segmentation/plot_boundary_merge.html#example-segmentation-plot-boundary-merge-py) to fix the remaining coins, and the background."
+    "That's pretty good! Some coins are perfectly segmented, with only one missing. We can't do much about the missing one (yet), but we can [*merge regions*](http://scikit-image.org/docs/dev/auto_examples/segmentation/plot_boundary_merge.html#example-segmentation-plot-boundary-merge-py) to fix the remaining coins, and the background. For that we need a *region adjacency graph*, or RAG."
    ]
   },
   {