The context within the screen IS where the boxes should display. Available contexts vary from screen to screen. Post edit screen contexts include ‘normal’, ‘side’, and ‘advanced’. Comments screen contexts include ‘normal’ and ‘side’. Menus meta boxes (accordion sections) all use the ‘side’ context. Global default is ‘advanced’.
So it is the place you are removing the box from.
https://codex.wordpress.org/Function_Reference/remove_meta_box