What is this Box above my sheet?

Hello everyone,

Can anyone tell me what this big box is and how I can get rid of it?
Capture.PNG

Thank you

Columns of your sheet are grouped on 7 nested levels.
Use
>Data>Group and Outline>Remove Outline to get rid of that in one step. or
>Data>Group and Outline>Ungroup as often as needed/wanted.

(You probably used a related shortcut / HotKey inadvertently.)

THANK YOU!