Third cousins are two people who share at least one great-great-grandparent. They have parents who are second cousins, grandparents who are first cousins and great-grandparents who are siblings.Know More
Someone can also have a cousin who is so many times removed. The term "removed" describes the number of generations cousins are apart. For example, when a third cousin has a child, that offspring becomes a third cousin once removed to the parent's third cousin. The offspring of that child is a third cousin twice removed to the original third cousin. This pattern continues down the line, as each generation has children. The children of third cousins are fourth cousins.