Darkness literally means absence of light. Call it ignorance, depression, emptiness, hopelessness etc etc, basically it is absence of the its opposite, light.
The beauty of darkness is that, like we cannot appreciate happiness without having gone through sadness, we cannot appreciate light without having experienced darkness.
While cleaning my table today i found this quote on a old paper which can be used here..
Darwin Correspondence Project of University of Cambridge however refutes Darwin ever having said that. Anyways, the meaning behind the quote is more important.
Moral: Replace Darkness with light, sadness with happiness, bad with good. Adapt.
While the process happens, Enjoy it anyway.. This too shall not last forever!