c-u
> > >
In Cmd mode, c-u
denotes “Remove all characters between the cursor position and the beginning of the line.”
When in Visual mode, pressing :
inserts the range:
:'<,'>
Mapping with c-u
removes the range and then executes the following command:
nnoremap foo :<C-u>bar
https://vi.stackexchange.com/questions/9751/understanding-ctrl-u-combination