What is the legal definition of an apostate (Murtadd)?

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The apostate is defined as one who abandons the religion of Islam and returns to disbelief (Kufr). This is substantiated by the decree of Allah: Whoever reverts from among you to his religion and dies in that state, their deeds are void in this life and the Hereafter, and those are the inhabitants of the Fire, therein abiding eternally (Quran 2:217). Furthermore, the Prophet, peace be upon him, stated: Whoever changes his religion, kill him. The scholarly consensus holds that executing the apostate is obligatory, a ruling narrated from Abu Bakr, Umar, Uthman, Ali, Mu'adh, Abu Musa, Ibn Abbas, Khalid, and others, and their lack of denial confirms the consensus (Ijma').