move_base_simple/goal - geometry_msgs/PoseStamped
It is a topic (non-action type) on which one can post a goal if he does not want to monitor its status (success or not) after posting.
initialpose - geometry_msgs/PoseWithCovarianceStamped
It is used to re-state the current position of the robot in the map if the robot seems lost. 2d pose estimate in rviz does this.
Move_base/local_costmap/inflated_obstacles - nav_msgs/GridCells
It specifies the cells in the map grid that are considered occupied due to the inflation radius of the robot. The inflation radius of the turtlebot is mentioned in turtlebot_navigation/config/local_costmap_params.yaml
move_base/local_costmap/obstacles - nav_msgs/GridCells
It specifies the cells in the map grid that are occupied by obstacles.
move_base/local_costmap/robot_footprint - geometry_msgs/PolygonStamped
In a map, the the robot is represented as a polygon which is called 'footprint' of a robot. This topic lists the points on the circumference of the polygon that form the footprint.
move_base/NavfnROS/plan - nav_msgs/Path
Once you give a nav goal the robot marks a path along which it has to move to reach the goal point (shown as a thin gree line in rviz). This topic lists the points in the local costmap that lie on the path.
Read more here, here, here and here.
