There are so many terms for the different moons we see at certain points of the year: New moon, Super Moon, Blood Moon, Black moon, etc. I like the Black moon the most.
More often than not, when people speak about a Black moon, they're referring to a second new moon in a calendar month. Typically, there is just one new moon per calendar month. However, every 29 months, there is a second moon-- a Black moon. February is the only month where a second new moon won't occur.
People also call this second moon in a month, a Blue moon. The names are analogous. Sometimes, people will use the term Black moon to denote a month that has no full moon at all.
This only occurs in February, since it's such a short month, and will only ever happen every twenty years. In Wiccan culture, some believe a Black moon is very powerful.