A jihad is a holy war against infidels, which means against anyone who doesn't think Islam is the true religion. Jihad is mentioned numerous times in the Koran. Many of the wars fought right after Islam was established in the seventh century were described as jihads. In the 19th and 20th centuries, the idea of jihad was revived by radicals and used to justify attacks on Muslims and non-Muslims alike.

For a Muslim fundamentalist, jihad is a win-win situation. If you conquer your enemies and live, Allah will give you the spoils of victory. If you die, you die a martyr and go to a blissful afterlife.