Officially...nothing. Astronomers do not use the term Blood Moon. The best I could find on the use of the term Blood Moon is in biblical prophesies. More on this here:
All lunar eclipses appear reddish/brownish/orangish during totality, so I guess you can say the Moon sort of looks blood colorish. But that's a big stretch. Here's a picture of a typical lunar eclipse in totality.
That's a far cry from the color of blood. To conclude, the term Blood Moon is not used in astronomy and it's not a term you'll see me use again, unless I have to debunk some crazy claim or lie regarding lunar eclipses. :-)