when in doubt, to the dictionary!!
dark·ness /ˈdɑrknɪs/ - [dahrk-nis]
–noun 1. the state or quality of being dark: The room was in total darkness.
2. absence or deficiency of light: the darkness of night.
3. wickedness or evil: Satan, the prince of darkness.
4. obscurity; concealment: The darkness of the metaphor destroyed its effectiveness.
5. lack of knowledge or enlightenment: heathen darkness.
6. lack of sight; blindness.
;P i personally endorse deffination number 2. There are many different turns this thread could take, b/c darkness is used differently depending on the situation/story/ whatnot; its something different in religion, fiction, science, etc, and depending on what you want to know, or what you ask of other peoples' views on the matter, they will tell you something different.
@Dark___edge : if you don't tell us what you specifically don't understand, we won't really be able to help you =P