Cousin once removed.
Your mother's cousin's son is your second cousin.
Your Uncle's son is your first cousin.
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.
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...
2nd cousin once removed
Your great aunt's son is first cousin to one of your parents, and first cousin once removed to you.
Well, your cousin's brother is also your cousin, and a cousin's son is also your cousin.
Your great aunt's son is your parent's first cousin and your first your cousin, once removed.
Your great aunt's son is first cousin to one of your parents, and first cousin once removed to you.
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.