What does the title "Black Moon" mean?

Something mythological strongly associated with "Lilith" (note the similarity to the name "Lily"). That's the general explication that works for me; exactly what it is is still not so clear.

Perhaps the best explanation I've found is: "The Moon travels along an elliptical path around the Earth. An ellipse has two focal points, and the other focal point, not occupied by the Earth has been called the Dark Moon, the Black Moon or Lilith." (The source goes on to explain this is known to not be strictly accurate, but...)

Another explanation is it's an eclipse of the moon, when the earth's shadow crosses the moon and the moon is briefly completely dark.

There are also religious connotations, some of which have survived in the form of the "Black Madonna".

And there are connotations (assuming the "Black Moon" is the same as "Lilith") of involvement in a great war between the sexes, with the "Great Goddess" (or "Mother Goddess" or "Mother Earth") being overcome by various patriarchal societies and religions.