Usage of the term

The term Jihad used without any qualifiers is generally understood to be referring to war on behalf of Islam. Within Islamic jurisprudence Jihad is the only form of warfare permissible under Islamic law, and may be declared against apostates, rebels, highway robbers, violent groups, unIslamic leaders or military exertion against non-Muslim combatants but there are other ways to perform jihad as well including civil disobedience. In broader usage and interpretation, the term has accrued both violent and non-violent meanings. It can imply striving to live a moral and virtuous life, spreading and defending Islam as well as fighting injustice and oppression, among other things. In the languages of non-Islamic cultures, the term is usually used to refer to Muslim 'Holy War' or any violent strife invoking Allah.
The primary aim of jihad is not always the conversion of non-Muslims to Islam by force, but rather the expansion and defense of the Islamic state. Thereafter, non-Muslims within the Islamic state would be encouraged to convert pursuant to Sharia Law and the Dhimmi system. In the classical manuals of Islamic jurisprudence, the rules associated with armed warfare are covered at great length. Such rules include not killing women, children and non-combatants, as well as not damaging cultivated or residential areas. More recently, modern Muslims have tried to re-interpret the Islamic sources, stressing that Jihad is essentially defensive warfare aimed at protecting Muslims and Islam. Although some Islamic scholars have differered on the implementation of Jihad, there is consensus amongst them that the concept of jihad will always include armed struggle against persecution and oppression. Some Muslims believe that the Prophet Muhammad regarded the inner struggle for faith a greater Jihad than even fighting [by force] in the way of God.
Jihad has also been applied to offensive, aggressive warfare, as exemplified by early movements like the Kharijites and the contemporary Egyptian Islamic Jihad organization (which assassinated Anwar Al Sadat) as well as Jihad organizations in Lebanon, the Gulf states, and Indonesia. When used to describe warfare between Islamic groups or individuals, such as Al-Qaeda's attacks on civilians in Iraq, perpetrators of violence often cite collaboration with non-Islamic powers as a justification. The terrorist attacks like September 11, 2001 planned and executed by radical Islamic fundamentalists have not been sanctioned by more centrist groups of Muslims.
Middle East Historian Bernard Lewis points out that some modern Muslims sources try to portray jihad in a spiritual and moral sense when addressing non-Muslims. Muslims tell people that they shouldn't try to define jihad by the actions of extremists, but at the balanced Muslims. For most of the fourteen centuries of recorded Muslim history, jihad was most commonly interpreted to mean armed struggle for the defense or advancement of Muslim power. In Muslim tradition, the world is divided into two houses: the House of Islamic Peace (Dar al-Salam), in which Muslim governments rule and Muslim law prevails, and the House of War (Dar al-Harb), the rest of the world, still inhabited and, more important, ruled by infidels. The presumption is that that by natural law these domains will compete and fighting is inevitable therefore the duty of jihad will continue, interrupted only by truces, until all the world either adopts the Muslim faith or submits to Muslim rule. Those who fight in the jihad qualify for rewards in both worlds—booty in this one, paradise in the next. For most of the recorded history of Islam, from the lifetime of the Prophet Muhammad onward, the word jihad was used in a primarily military sense.
The word itself is recorded in English since 1869, in the Muslim sense, and has been used for any doctrinal crusade since c. 1880.
In Modern Standard Arabic, jihad is one of the correct terms for a struggle for any cause, violent or not, religious or secular (though كفاح kifāḥ is also used). For instance, Mahatma Gandhi's struggle for Indian independence is called a "jihad" in Modern Standard Arabic (as well as many other dialects of Arabic) even though it was neither an Islamic struggle nor conducted violently; the same terminology is applied to the fight for women's liberation.
When Muslim populations are attacked on the basis of religion, Jihad becomes mandatory on the government of that particular state (and all Muslims) until all hostile forces are either eliminated or negotiated out of the occupied land. If the threat continues to persist, the Islamic State may have to eliminate the threat through force.