It forms the first part of the surgeon's knot and both sides of a double fisherman's knot. According to The Ashley Book of Knots, "A double overhand knot tied in a cat-o'-nine-tails is termed a blood knot."
This knot is an essential component of the surgeon's knot and forms part of both a double fisherman's knot.  The Ashley Book of Knots identifies it as a "blood knot" when tied in a cat-o'-nine-tails fashion.