The dates of the 2015 blood moons are April 4th and September 15th. These dates are the final two of the 2014 to 2015 Lunar Tetrad, the first two being April 15th and October 8th of 2014.
The term "Blood Moon" is sometimes used to describe a Total Lunar Eclipse. The red glow occurs when the earth casts its shadow on the full moon before eclipsing it. The phrase "Lunar Tetrad" describes the occurrence of four total eclipses in a row. These tetrads are rare, and according to NASA, the century of 2001 to 2100 contains a total of eight. The tetrads hold special significance for some people, as they coincide with important Jewish festivals.