His nephew .
Your fathers brothers are your uncles. You are their nephew, or niece.
There is no proper term for this particular familial place. I would suggest just his name or your step-father's grandson.
Your father's great nephew is the son of your father's niece or nephew. Your father's nieces and nephews are your first cousins. Their children are your father's great nieces and great nephews, and are your first cousins, once removed.
Your father's nephew is your first cousin. Your first cousin's son, which is your first cousin once removed.
First cousin, once removed. He is your nephew.
Your dad's nephew is your first cousin, his children are your first cousins once removed.
Your nephew's nephew is the son of one of your nephew's brothers or sisters. He is your great nephew.
First cousin, once removed. Your parent on that side would be a first cousin to the nephew. If the nephew has children, they will be your second cousins. (Of course, your great uncle's nephew could also be your father).
Your mom's elder sister is your aunt; the son of your aunt is your cousin, and the daughter of your cousin is your cousin once removed.
In English language terms for family relationships, there is no relationship called "nephew once removed." The son of your nephew is your great nephew.
cousin
Nephew It's actually himself. No brothers or sisters and his dad's son.