The guys at EarthSky.org took it upon themselves to answer that question. You should read the whole article, really, but for those of us with shorter attention spans, here’s the bullet point:
It’s a total lunar eclipse. The phrase blood moon is new (as of this year) to astronomers, but 2 pastors wrote a book that referred to blood moons last year. They use the phrase to refer to the full moons of the upcoming tetrad (four successive total lunar eclipses, with no partial lunar eclipses in between, each of which is separated from the other by six lunar months.) But, um, they’re also suggesting that these next lunar eclipses are signs of end times.
Fun Fact: There are a total of 8 tetrads in the 21st century (2001 to 2100.) Smart money says the earth will still be here after all of them.