The capitation tax, which is levied by Muslim rulers upon subjects who are of a different faith, but claim protection (aman). It is founded upon a direct injunction of the Qur’an: “Make was upon such of those, to whom the Scriptures have been given, as believe not in God or in the last day and forbid not that which God and his Apostles have forbidden and who profess not the profession of truth until they pay tribute (jizyah) out of their hand, and they be humbled.
According to the Hidayah (vol. ii. p. 211), jizyah is of two kinds: that which is established voluntarily, and that which is enforced. The usual rate is one dinar for every male person, females and children being exempt according to Abu Hanifah, but included by Ash Shafi’i. It should be imposed upon Jews, and Christians, and Magians, but it should not be accepted from the Arabian idolators, or from apostates, who should be killed. But from idolators of other countries than Arabia it may be accepted. It should not be levied upon some monks, or hermits, or paupers, or slaves. He who pays the capitation tax and obtains protection from the Muslim state is called a zimmi.
Based on Hughes, Dictionary of Islam