This is the official manual for the latest Org-mode release.
If you use Org mode extensively, you may end up with enough TODO items that it starts to make sense to prioritize them. Prioritizing can be done by placing a priority cookie into the headline of a TODO item, like this
*** TODO [#A] Write letter to Sam Fortune
By default, Org mode supports three priorities: ‘A’, ‘B’, and
‘C’. ‘A’ is the highest priority. An entry without a cookie is
treated just like priority ‘B’. Priorities make a difference only for
sorting in the agenda (see Weekly/daily agenda); outside the agenda, they
have no inherent meaning to Org mode. The cookies can be highlighted with
special faces by customizing
Priorities can be attached to any outline node; they do not need to be TODO items.
You can change the range of allowed priorities by setting the options
org-default-priority. For an individual buffer, you may set
these values (highest, lowest, default) like this (please make sure that
the highest priority is earlier in the alphabet than the lowest
#+PRIORITIES: A C B
 See also the option