Any right, privilege, or possession to which a person is entitled by birth, such as an estate descendible by law to an heir, or civil liberty under a free constitution; esp. the rights or inheritance of the first born.

People born to Quaker parents used to be automatically members from birth (this is still the case in some countries). This is still possible but most people join after reflecting on membership for themselves. You can join at any age.

a right or privilege that you are entitled to at birth; "free public education is the birthright of every American child"

an inheritance coming by right of birth (especially by primogeniture)

personal characteristics that are inherited at birth

a right you have because of the family or country or culture you are born into

The special inheritance rights of the first-born son giving him claim to the bulk of the ancestral property.