Explanation

Everyone belongs to a blood group and there are four different ones - A, B, AB and O. If you have a protein called the rhesus factor in your blood, your blood group is called positive, if you don't, your blood group is called negative.

Although lots of people don't know which blood group they belong to, it's important if you are having a blood transfusion. This is because if your blood group is different from the one that the donated blood belongs to, your body might not accept the blood.