He or she would be your forth cousin.
second cousin once removed
Your mother's first cousin's son is your second cousin. Her first cousin's son's son (her first cousin's grandson) is your second cousin, once removed.
That would be your second cousin.
Your first cousin's son is your first cousin, once removed. Your second cousin's son is your second cousin, once removed.
The son of your father's first cousin is your second cousin .
Your son and your 1st cousin's child are 2nd cousins.
Your father's first cousin's son is your second cousin. Your father's second cousin's son is your third cousin. If your are asking about your fathers cousins who are in a removed cousin relationship to your father, their relationship to you be more complex, with two different possibilities in each case.
Your uncle's son is your (first) cousin.
A person's relationship to the child of a cousin is the same as that person's relationship to the cousin, with one remove added. If your cousin is your first cousin, then his son is your first cousin, once removed. If your cousin is your second cousin, then his son is your second cousin, once removed. If your cousin is your first cousin, once removed, then his son is your first cousin, twice removed.
Your cousin's children are your second cousins
The son of your First Cousin Once Removed, is your First Cousin Twice Removed.
He would be your son's third cousin.
You will be his aunt.