Jihad
An Arabic word meaning struggle, running from private moral effort to sanctioned warfare, and fought over hardest by Muslims themselves.
Jihad does not mean holy war. It means striving or exertion, and the Quranic phrase it usually appears in is jihad fi sabil Allah, struggle in the path of God. Arabic has a perfectly good phrase for holy war, harb muqaddasa, and classical Islamic sources essentially never use it. This is not a technicality. The whole political history of the word turns on the fact that it covers a spectrum, and that whoever gets to define where on that spectrum a given fight belongs is exercising enormous authority.
What the jurists actually said
Classical Islamic law treated armed jihad as a collective obligation, fard kifaya, meaning that if enough of the community discharged it the rest were excused. It became an individual obligation, fard ayn, binding on everyone including women and slaves, only when Muslim territory was invaded. That distinction is the hinge on which every modern argument turns.
The jurists also attached conditions. Armed jihad had to be declared by legitimate authority, the caliph or a recognized imam. Non-combatants, meaning women, children, the old, monks, and farmers, were not to be killed. Terms of surrender, once offered, bound the Muslim side. Trees and livestock were not to be destroyed wantonly. These rules were violated constantly, as the laws of war always are, but they existed and scholars enforced them rhetorically.
There is also the famous report in which the Prophet, returning from battle, tells his companions they have come from the lesser jihad to the greater jihad, the struggle against the self. Sufis built centuries of spiritual literature on it. Hadith specialists generally classify the report as weak, meaning poorly attested. Both facts are true at once and both get weaponized.
The institution on the ground
The frontier had architecture. A ribat was a fortified post where volunteers went to combine garrison duty with prayer and study, part barracks and part monastery, strung along the coasts of North Africa and the Central Asian marches. Serving a stint at a ribat was a devotional act. It is the clearest illustration of how the martial and the spiritual senses of the word coexisted rather than competing.
Jihad was also revived deliberately as propaganda. Twelfth-century preachers in Damascus and Aleppo used it to shame Muslim rulers into fighting the Crusader states rather than each other, and it worked well enough to produce Saladin.
Who declares it now
The classical system had an answer to the authority question, and in 1924 the answer disappeared. When Turkey abolished the caliphate there was no longer any office that could declare jihad in the way the jurists required. The vacuum was filled by people with no traditional standing to fill it.
Sayyid Qutb argued that nominally Muslim rulers had reverted to pagan ignorance and could therefore be fought. Muhammad abd al-Salam Faraj called armed jihad the neglected duty in a 1981 pamphlet circulated among the men who assassinated Anwar Sadat. Osama bin Laden issued declarations in 1996 and 1998 asserting an individual obligation on every Muslim to kill Americans, and he had no scholarly credentials of any kind. The overwhelming majority of established ulama rejected these claims as usurpation of an authority that was not theirs.
Why the distinction matters
Western usage collapsed jihad into terrorism, which hands the radicals exactly what they want: recognition as the authentic voice of the tradition. The live argument is not between Islam and the West. It is between a legal tradition that hedged warfare with conditions and a modern movement that discarded the conditions and kept the word.