Just about any other blood relative who isn’t your sibling, ancestor, aunt or uncle is your cousin. To determine your degree of cousinhood—first, second, third, fourth—you need to identify the ancestor you share with your cousin, and how many generations separate each of you from that ancestor. Your second cousins are the children of your parents’ first cousins. Take a look at your family tree, and you’ll see that you and your second cousins have the same great-grandparents. You typically share 3.125 percent of your second cousin’s DNA.

Source: Family Tree