우울 is melancholy. The literature definition is melancholy, and medical definition is depressed state of mind. If it is severe ailement, it is 우울증, which is depression.
It is continuity of resentment state of mind, many geniuses in authorship are reported as melancholy men. Their way of writing had unique sensation which transmit the feeling of calm, resentful, and depressive manner. The readers know it is painful state of emotion, but they have experience of empathy and even entertained by appreciating it.
However, it is very dangerous state of mind, when medical sense of depression is prevalent and could not be healed in right time. People can suicide if melancholy deepened to challenge their body too.
It drives people to develop artistic power, but melancholy friends are worried by their intimate people, so is important understanding to the word 우울.