A is C's son. C and Q are sisters. Z is Q's mother. P is the son of Z. How is P related to A?

Let us systematically analyze the structural kinship links:
1. $A$ is the son of $C$. Therefore, $C$ is a parent of $A$.
2. $C$ and $Q$ are sisters, which implies $C$ is female, making her $A$ 's mother.
3. $Z$ is $Q$ 's mother, which means $Z$ is also the mother of $C$.
4. $P$ is the son of $Z$, meaning $P$ is the brother of $C$ and $Q$.

Since $P$ is the biological brother of $A$ 's mother ($C$), $P$ is the maternal uncle of $A$.