Harbi is a term of classical islamic law

Sharia

Sharia law, is the moral code and religious law of Islam. Sharia is derived from two primary sources of Islamic law: the precepts set forth in the Quran, and the example set by the Islamic prophet Muhammad in the Sunnah. Fiqh jurisprudence interprets and extends the application of sharia to...

, which refers to a non-Muslim

Muslim

A Muslim, also spelled Moslem, is an adherent of Islam, a monotheistic, Abrahamic religion based on the Quran, which Muslims consider the verbatim word of God as revealed to prophet Muhammad. "Muslim" is the Arabic term for "submitter" .Muslims believe that God is one and incomparable...

, who does not live under the condition of the dhimma. Harbi is counterterm to dhimmi

Dhimmi

A , is a non-Muslim subject of a state governed in accordance with sharia law. Linguistically, the word means "one whose responsibility has been taken". This has to be understood in the context of the definition of state in Islam...

. Sometimes the terms appear in the combination "kafir harbi" resp. "kafir dhimmi".

The harbi is the inhabitant of the dar al-harb (house of war). A harbi has no rights, not even the right to live. If a harbi wants to enter the territory of Islam (dar al-islam) he needs a safe-conduct

Safe-conduct

Safe conduct is the situation in time of international conflict or war where one state, a party to such conflict, issues to a person, usually an enemy state's subject, a pass or document to allow the enemy alien to traverse its territory without harassment, bodily harm, or fear of death. Safe...

 called aman.

According to the Middle East Media Research Institute

Middle East Media Research Institute

The Middle East Media Research Institute is a Middle Eastern not for profit press monitoring organization with headquarters located in Washington, DC. MEMRI was co-founded in 1998 by Yigal Carmon, a former colonel in the Israeli military intelligence and Meyrav Wurmser, an Israeli-born, American...

 Yusuf al-Qaradawi

Yusuf al-Qaradawi

Yusuf al-Qaradawi is a controversial Egyptian Islamic theologian. He is best known for his programme, ash-Shariah wal-Hayat , broadcast on Al Jazeera, which has an estimated audience of 60 million worldwide...

 said:

"It has been determined by Islamic law that the blood and property of people of Dar Al-Harb [the Domain of Disbelief where the battle for the domination of Islam should be waged] is not protected. Because they fight against and are hostile towards the Muslims, they annulled the protection of his blood and his property."http://memri.org/bin/articles.cgi?Page=archives&Area=sd&ID=SP54203

According to the Middle East Media Research Institute

Middle East Media Research Institute

The Middle East Media Research Institute is a Middle Eastern not for profit press monitoring organization with headquarters located in Washington, DC. MEMRI was co-founded in 1998 by Yigal Carmon, a former colonel in the Israeli military intelligence and Meyrav Wurmser, an Israeli-born, American...

 the Egyptian Grand-Mufti

Mufti

A mufti is a Sunni Islamic scholar who is an interpreter or expounder of Islamic law . In religious administrative terms, a mufti is roughly equivalent to a deacon to a Sunni population...

, Dr. Sheikh Ali Gomaa

Ali Gomaa

Sheikh Ali Goma'a is the Grand Mufti of Egypt through Dar al-Ifta al-Misriyyah succeeding Ahmad El-Tayeb. He has been called "one of the most widely respected jurists in the Sunni Muslim world," and described as "a highly promoted champion of moderate Islam," gender equality, and an "object of...

, said on Jihad

Jihad

Jihad , an Islamic term, is a religious duty of Muslims. In Arabic, the word jihād translates as a noun meaning "struggle". Jihad appears 41 times in the Quran and frequently in the idiomatic expression "striving in the way of God ". A person engaged in jihad is called a mujahid; the plural is...

and killing harbis:

Question: "Is it permitted to kill an Israeli traveling outside the borders of his land?"

Sheikh Gum'a: "Yes, it is permitted to kill him, because he is a Harbi and the Harbi spreads corruption throughout the face of the earth."http://www.memri.org/bin/articles.cgi?Area=sd&ID=SP58003

However, it must be noted that this was in the context of a question asking for an Arabic response to a perceived corresponding failure of Israelis to distinguish between civilians and militants in its attacks.