This is the 1035th most frequent Russian word.
крови
"Крови" means "of blood" or "blood's" in English.
The genitive form "крови" indicates possession or part of a whole.
У меня на руке капля крови.
I have a drop of blood on my hand.
Here, "крови" is used metaphorically to signify origin or ancestry.
Она была человеком благородных кровей.
She was a person of noble blood.
The genitive form "крови" is used to describe coverage or association.