What is the SN number in USA?

Could you please elaborate on the significance and purpose of the SN number in the context of the United States? Is it a unique identifier assigned to a specific product, service, or individual? If so, what entities are responsible for issuing and managing these numbers? Additionally, are there any regulations or standards that govern the use of SN numbers in the USA? Understanding the intricacies of this topic would greatly aid in clarifying its importance and relevance.