A fitri murtad is one who was born of Muslim parents (or at least one parent) and then rejects Islam. If he rejects Islam, then, according to the fatawa of our maraji (including Ayatullahs al-Khu'i and Khumayni) he is to be killed.
FITRI MURTADD
Meaning of FITRI MURTADD in English
Advanced Islamic English dictionary. Расширенный исламский словарь английского языка. 2012