What is the true meaning of jihad?

Jihad means "holy war" in the Islamic terminology. This is usually declared against infidels in the defense of the Islamic faith. This is somewhat analogous and synonymous with the Holy Crusades. In fact, the Christians were in a crusade against the Muslims in a jihad to conquer the Holy Land. Whether or not it applies to extremist terrorism, that I cannot answer.

Despite having various meanings, Jihad is generally believed to be a 'holy war'. A war in the name of Allah. It is used to protect fellow Muslims and in older days, it was used for rescue and retaliation. Nowadays, Jihad is connotated to aggression - mostly towards Westerners, as some radical Muslims tend to hate the free-thinking and liberal West.