It means obtaining that which is due to him by right of his birth.
A birthright is a right bestowed upon someone simply by them being born a specific person. For example, the son of a king is born as a prince. It is his birthright to be a prince simply because he was born the son of a king. Taking this example a little further, the first born son of a king will likely become king himself one day (as traditionally this honour passes to the first born male). When he becomes king he could describe this as "coming into his birthright".
Life and freedom are the birthright of every human.
Birthright Israel was created in 1994.
Birthright - band - ended in 2000.
Birthright - band - was created in 1994.
Birthright - Doctor Who - was created in 1993.
The duration of Birthright - film - is 1.8 hours.
The story may be apocryphal, but the implication is that knowledge is not obtained by birthright.
Birthright - film - was created on 2010-10-24.
Birthright Campaign Setting was created in 1995.
Birthright - Diablo novel - was created in 2006-10.
Birthright - Diablo novel - has 326 pages.
His Birthright - 1918 was released on: USA: 8 September 1918