A second cousin is a someone who shares a great-grandparent with you.

Who is your second cousin?

Your second cousin is the grandchild of your great-uncle or -aunt. Your great-uncle is in the same generation as your grandparents, which means you are in the same generation as his grandchild.

Are second cousins blood related?

Who Are Second Cousins? Second cousins share a great-grandparent, either maternal or paternal. You and your second cousins have the same great-grandparents, but not the same grandparents. ... If members of your family were adopted, your second cousins may not be blood related to you.