What is the `plugin` command in `~.urdf.xacro` file?

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Hello, I'm working on ROS melodic of Ubuntu 18.04.

I'm having modified the ~.urdf.xacro file to attach a LiDAR sensor to mobile robot (on simulator).

But it already has one kind of sonar sensor default.

I tried to convert it to LiDAR sensor, and I faced with the following in ~.urdf.xacro file :

     <plugin name="gazebo_ros_${name}_controller" filename="libhector_gazebo_ros_sonar.so">
      <gaussianNoise>0.005</gaussianNoise>
      <topicName>${ros_topic}</topicName>
      <frameId>${name}_link</frameId>
    </plugin>
 <plugin name="gazebo_ros_${name}_controller" filename="libgazebo_ros_laser.so">
    <topicName>/scan</topicName>
     <frameName>${name}_link</frameName>
 </plugin>

So, what does the plugin command do?

In the case of LiDAR sensor, I've never seen the above plugin codes at least so far.

If anyone who knows it, would you please give me advice?

Thanks in advance. :)