Your second cousin and your son are second cousins, once removed.
It's your second cousin (:
The son of your second cousin is your second cousin, once removed. You are also his second cousin, once removed.
Your mother's cousin's son is your second cousin.
Second Cousin
You and your second cousin's son are second cousins, once removed, to each other.
First cousin, once removed. Second cousin
Your father's first cousin is your son's first cousin twice removed. Your father's second cousin is your son's second cousin, twice removed. And so forth...
Your son and your first cousin's son are second cousins to each other. Your first cousin's son is also YOUR first cousin, once removed.
Your first cousin's son and your children are second cousins to each other. Your second cousin's son and your children are third cousins to each other.
Your grandmother is first cousins with cousin. Your parent would be the second cousin of the cousin's son. That would make you second cousins once removed.
Your grandfather's niece is a first cousin of one of your parents. Her son is your second cousin.
Your grandfather's niece is a first cousin of one of your parents. Her son is your second cousin.