尊姓 is a formal, polite noun used to ask someone's surname in a respectful way, equivalent to 'your esteemed surname' in English. It appears in set phrases like 尊姓大名 (your full name) and is typical in formal introductions, business settings, or when addressing elders or superiors. Unlike the more common 你姓什么, 尊姓 carries a tone of deference.