1. The specific date on which a person officially assumes or begins their role in a position of authority, duty, or employment
The president's date of office is January 20th.
A data de posse do presidente é 20 de janeiro.
2. The official starting date of a term in public office or governmental position
The new governor will begin her date of office next month.
A nova governadora começará sua data de posse no próximo mês.