M-x presents you a list of interactive commands. They are lisp commands, but the user is concerned with their name when looking for a command, so displaying command names with spaces instead of dashes can make a more readable, cleaner presentation.

So instead of this:

delete-active-region
delete-char (<delete>)
delete-directory
delete-file-local-variable
delete-frame (C-x 5 0)
delete-matching-lines (flush-lines)
delete-other-frames (C-x 5 1)
delete-other-windows-vertically
delete-region
delete-trailing-whitespace

it would look like this:

delete active region
delete char (<delete>)
delete directory
delete file local variable
delete frame (C- x 5 0)
delete matching lines (flush lines)
delete other frames (C-x 5 1)
delete other windows vertically
delete region
delete trailing whitespace