A second cousin is a relative who shares a common ancestor that is at least two generations away, such as a great-grandparent. To be more specific, second cousins are the children of your parents first cousins. You and your second cousins have the same great-grandparents. To calculate cousin relationships, you can count how many "greats" are in your common ancestors title and add 1 to find out what number cousin your relative is. For example, if the common ancestor is your cousins great-grandparent, you add 1 to the number of "greats" in the title, which is 1, to get 2, so this is your second cousin.