주민등록증 is a national identification card in South Korea that serves as proof of a person's identity and residency. It is issued to all citizens aged 17 and older and contains essential information such as the individual's name, date of birth, and address. The card is important for various administrative purposes, including voting, accessing government services, and verifying identity in financial transactions. It plays a crucial role in maintaining accurate population records and ensuring that residents can access their rights and responsibilities within the country.