A formal or explicit promise, often between people or groups. Can imply a binding commitment.
He is a person who keeps his promises.
結婚は大切な約束事です。
Marriage is an important vow.
A socially or mutually agreed rule, convention, or resolution. Often used in contexts like meetings, organizations, or shared understandings.
会議で新しい約束事が決まった。
A new rule was decided at the meeting.
社会の約束事に従う。
Follow the conventions of society.