A half first cousin is a person who shares one grandparent with you, as opposed to full cousins who share two grandparents. This happens when the parents of the two half-cousins are half-siblings. For example, if your grandmother is not related to you, but your grandfather is, then your first cousins are your half cousins. Half cousins share around half the normal amount of DNA as full cousins. However, DNA doesn’t follow strict averages, so half of the first cousins can indeed share the same amount of DNA (even more in some cases) than full first cousins. It should be noted that being half cousins should not lessen the bond between two people, and most half cousins treat each other no differently from their full cousins.