Path Planning - Rviz - Gazebo

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Hi, I am doing Robot Navigation using Gazebo and Rviz. I used the 2D Nav goal in Rviz to select the goal position of the robot. When the robot starts moving I see a strange square box with different colors that are surrounded by the robot as you see in the picture. I don't know what does that box means.

I know how the local and global costmaps have been generated. But I have no idea if that is related to the costmaps.

Can anyone please explain to me technically what does that square box with different colors that are around that robot means??