Just found the term "dritter Grad der Blutsverwandtschaft" in a 1793 marriage record of northern Alsace. I know that I can translate this to "third degree or grade of blood relationship", but that does not really help me. Are we talking about second cousins? third cousins?
Added after some reflection: The two men so identified were members of the bride's wedding party, but neither was the groom. I have not seen such identifications in any other records from the era and area. Why would they be added here?