launch file for a nox simular robot

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I am studying the nox robot software on Github, as I am building a similar robot. Can anyone tell me what is the meaning of the first line in the launch file below?

"robot_description" doesn't occur anywhere in the c++ file, nor in any other file in the package. I cannot find "prtype_wa.urdf" in the package, nor anywhere in the ROS libraries. Does anyone know what this line is supposed to do? (https://github.com/RBinsonB/Nox_robot/)

<launch>
                <!--  ************** Odometry ***************  -->
    <param name="robot_description" command="cat $(find ptype_wa_description)/urdf/ptype_wa.urdf" />

    <node name="joint_state_publisher" pkg="joint_state_publisher" type="joint_state_publisher">
        <rosparam param="source_list">["odom_comm/joint_states"] </rosparam>
    </node>
    <node name="robot_state_publisher" pkg="robot_state_publisher" type="state_publisher" />                

    <node name="odom_comm" pkg="ptype_wa" type="odom_comm" />
    <node name="odom_broadcaster_ptype_wa" pkg="ptype_wa" type="odom_broadcaster_ptype_wa" />


                <!--  ************** Sensors ***************  -->
    <node name="urg_node" pkg="urg_node" type="urg_node" output="screen">
        <param name="ip_address" value="192.168.1.70"/>
        <param name="frame_id" value="/base_laser"/>
    </node>


                <!--  ************** gmapping ***************  -->
    <node name="slam_gmapping" pkg="gmapping" type="slam_gmapping" output="screen"/>


            <!--  ************** Navigation ***************  -->
    <node pkg="move_base" type="move_base" respawn="false" name="move_base" output="screen">
        <rosparam file="$(find ptype_wa_control)/cfg/costmap_common_params.yaml" command="load" ns="global_costmap" />
        <rosparam file="$(find ptype_wa_control)/cfg/costmap_common_params.yaml" command="load" ns="local_costmap" />
        <rosparam file="$(find ptype_wa_control)/cfg/local_costmap_params.yaml" command="load" />
        <rosparam file="$(find ptype_wa_control)/cfg/global_costmap_params.yaml" command="load" />
        <rosparam file="$(find ptype_wa_control)/cfg/teb_local_planner_params.yaml" command="load" />

        <param name="base_global_planner" value="global_planner/GlobalPlanner" />
        <param name="planner_frequency" value="1.0" />
        <param name="planner_patience" value="5.0" />

        <param name="base_local_planner" value="teb_local_planner/TebLocalPlannerROS" />
        <param name="controller_frequency" value="5.0" />
        <param name="controller_patience" value="15.0" />

      <param name="clearing_rotation_allowed" value="false" /> <!-- Our carlike robot is not able to rotate in place -->
    </node>

    <node name="ptype_wa_controller" pkg="ptype_wa_control" type="ptype_wa_controller" output="screen" />


                <!--  ************* Visualisation **************  -->
    <node name="rviz" pkg="rviz" type="rviz" args="-d $(find ptype_wa_control)/cfg/rviz_slam.rviz" required="true" />

</launch>

"robot_description" is also used in:

<launch>
                <!--  ************** Odometry ***************  -->
    <arg name="gui" default="True" />
    <param name="use_gui" value="$(arg gui)"/>
    <param name="robot_description" command="cat $(find nox_description)/urdf/nox.urdf" />

    <node name="joint_state_publisher" pkg="joint_state_publisher" type="joint_state_publisher" />

    <node name="robot_state_publisher" pkg="robot_state_publisher" type="state_publisher" />

    <node name="serial_node" pkg="rosserial_python" type="serial_node.py">
        <param name="port" value="/dev/ttyACM0"/>
    </node>

    <node name="nox_controller" pkg="nox" type="nox_controller">
        <param name="publish_tf" value="true" />
            <param name="publish_rate" value="10.0" />
            <param name="linear_scale_positive" value="1.025" />
            <param name="linear_scale_negative" value="1.025" />
            <param name="angular_scale_positive" value="1.078" />
            <param name="angular_scale_negative" value="1.078" />
        <param name="angular_scale_accel" value="0.0" />
    </node> 

                <!--  ************** Sensors ***************  -->
    <include file="$(find freenect_launch)/launch/freenect.launch" />
    <node name="depthimage_to_laserscan" pkg="depthimage_to_laserscan" type="depthimage_to_laserscan">
        <remap from="image" to="camera/depth/image_raw" />
    </node>

</launch>