He could be your brother. He could be a first cousin. If the uncle married into the family (Married the sister of one of your parents), the brother would not be related in any way and neither would his son.
Your mother's brother is your uncle.The children of your aunts and uncles are your first cousins.
Your brother's daughter's daughter is your great niece.
The English word uncle unfortunately does not differentiate between father's brother and mother's (usually younger)brother. Both are uncles! A tamil girl would marry her mother's brother - uncle. A mother's brother is called மாமன் (maaman)
The son of either your sister or your brother is your nephew. The English language does not make a distinction in that.
Your uncle's son is your first cousin.
It means you have (or had) at least two uncles and at least two great-uncles, and that is all it means.
Your mother's brother is your uncle. Your uncle is your son's great uncle. You are the nephew of your mother's brother. Your son is his great nephew.
nephew
Nephew
Your mother's brother's son would be her nephew and your cousin.
Your father's brother's son (or daughter) is your first cousin, and is usually called by name.
Nieces.