The most ethical and appropriate course of action, unbiased and
   respectful of others, guided by conscience and accomplished without the
   motive of recognition or recompense.

Other definitions

   An action "that is the expression of one's inner voice translated into
   action." "We thus act with the most justness when we follow our
   conscience, respecting the rules of our countries, and not harming or
   impairing others." "It consists of knowing exactly what our obligations
   are, and accomplishing it to the best of our ability without
   consideration of success, renown, reward, etc."
   [1]https://www.grainesdepaix.org/en/resources/peace-dictionary/just-act
   ions-1#:~:text=RSS,motive%20of%20recognition%20or%20recompense.

References

   1. https://www.grainesdepaix.org/en/resources/peace-dictionary/just-actions-1#:~:text=RSS,motive of recognition or recompense