A person who guarantees another person's identity and (often) legal or financial responsibility; commonly required for rental contracts or certain administrative procedures.
このアパートを借りるには身元保証人が必要です。
You need a guarantor to rent this apartment.
会社が外国人社員のために身元保証人になることがある。
A company may act as guarantor for a foreign employee.
病院の入院手続きで身元保証人の連絡先を聞かれた。
They asked for the contact information of a guarantor during the hospital admission procedure.