The term black moon is a contemporary term for a second new moon in a month or a season; the dark of the moon’s (or new moon) equivalent of the term blue moon, which is applied to the full moon.
Like the blue moon, the details for the definition of the term black moon used by witches and other magic-users who work with the energy of the moon vary between traditions. The black moon may be the second dark moon or new moon in a one month period or it may refer to a month in which there is no full moon. February is the only month in which a full moon may be absent due to its shortened length. It is also impossible for there to be two new moons in the month of February, also due to its length.
The term “black moon” is also occasionally used synonymously with the term the dark moon to refer to the time of the month when the moon is not visible in the sky.
Some say that no magic should be worked on the black moon. Others believe that the moon’s energy is highly amplified at this time. The dark of the moon is a powerful time for banishing and binding, but the new moon, which follows quickly afterward is a potent time for drawing magick and new beginnings.