It could be your son. It could be your nephew as well.
It could be no relationship to you at all.
The question is do you share a common ancestor? If you do not have a common ancestor, you are not related.
your uncles daughter would be your cousin
your cousin
Your son would be the uncle of his brother's son.
There is no specific relation. They're just a distant relative. But if you are very close to them, you would often call them your cousin, even though that isn't the case.
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.
You would be a great uncle, so they would be your great nephew
If your half-sister had a son that would be a half-nephew to you
A nephew is a cousin to his aunt's son.
your uncles son is your cousin
Your uncle's grandchild would be your second cousin because his grown son or daughter would be your first cousin.
His great uncle