There may be no actual relationship. Only if you share a common ancestor is there going to be a legal connection. If there is, they would be a fourth cousin.
your cousin
your uncles daughter would be your cousin
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.
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 son is your cousin
His great uncle
Your cousin in law
great uncle
Your fathers brothers are your uncles. You are their nephew, or niece.
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 son would be the uncle of his brother's son.