When in an Org buffer and the region is active, some commands will
apply to all the subtrees in the active region. For example, hitting
C-c C-s when multiple headlines are within the active region will
successively prompt you for a new schedule date and time. To disable
this, set the option org-loop-over-headlines-in-active-region to
non-t, activate the region and run the command normally.
org-agenda-loop-over-headlines-in-active-region is the equivalent
option of the agenda buffer, where you can also use bulk editing of
selected entries.
Not all commands can loop in the active region and what subtrees or headlines are considered can be refined: see the docstrings of these options for more details.