Blood law is a set of rules that families follow to decide who will inherit their property and power when the parents or household leader dies. It's like a game that families play to decide who gets what. Blood law is usually based on who is related to the person who died and how closely they are related.
Let's imagine that your family has a treasure chest full of toys, and your mom is the one who decides who gets the toys when she dies. If you have a brother, he might get some of the toys, but if you have a sister, she might get more of the toys. Your mom might also decide that a cousin or an aunt or uncle should get some of the toys because they are related to your family.
Blood law can also determine who will be the next leader of the family or the tribe. If your dad is the leader of your tribe, and he dies, blood law might say that his oldest son should become the new leader. Or, it might say that his sister's son should be the new leader instead.
Blood law is important because it helps families and communities stay organized and make decisions that are fair to everyone. It can also help prevent fights and arguments over who gets what when someone dies.