diff --git a/autoware_planning_msgs/msg/RoadSegments.msg b/autoware_planning_msgs/msg/RoadSegments.msg
index e9b2f07..a890647 100644
--- a/autoware_planning_msgs/msg/RoadSegments.msg
+++ b/autoware_planning_msgs/msg/RoadSegments.msg
@@ -1,3 +1,3 @@
 std_msgs/Header header
-Segment[] segments
+Segment[] segments # The segments/lanelets
 geometry_msgs/Pose pose
diff --git a/autoware_planning_msgs/msg/Segment.msg b/autoware_planning_msgs/msg/Segment.msg
index 05cdade..b8fce8f 100644
--- a/autoware_planning_msgs/msg/Segment.msg
+++ b/autoware_planning_msgs/msg/Segment.msg
@@ -1,3 +1,5 @@
+# Segments are similar to lanelets.
+
 uint16 id
 Linestring[2] linestrings
 int32[] successor_lanelet_id