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Output of ros2 node info: what are these publishers/subscribers?

I ran the following command, trying to find out more about my /gazebo node:

 user@ubuntu:~$ ros2 node info /gazebo
/gazebo
  Subscribers:
    /parameter_events: rcl_interfaces/ParameterEvent
  Publishers:
    /clock: rosgraph_msgs/Clock
    /parameter_events: rcl_interfaces/ParameterEvent
    /rosout: rcl_interfaces/Log
  Services:
    /gazebo/describe_parameters: rcl_interfaces/DescribeParameters
    /gazebo/get_parameter_types: rcl_interfaces/GetParameterTypes
    /gazebo/get_parameters: rcl_interfaces/GetParameters
    /gazebo/list_parameters: rcl_interfaces/ListParameters
    /gazebo/set_parameters: rcl_interfaces/SetParameters
    /gazebo/set_parameters_atomically: rcl_interfaces/SetParametersAtomically
    /pause_physics: std_srvs/Empty
    /reset_simulation: std_srvs/Empty
    /reset_world: std_srvs/Empty
    /unpause_physics: std_srvs/Empty

I don't really understand the output. I understand that /gazebo is subscribing to the topic /parameter_events, but what is rcl_interfaces/ParameterEvent? I thought it was a node that was publishing to /parameter_events, but it doesn't show up when I run ros2 node list and it also doesn't appear as a node on rqt_graph.

I also thought that it might be the location of a file, so I went to search in my ros2 workspace, but I didn't find anything with the same name.

What is it, really?