What does jihad mean according to the Quran?
Jihad means struggle under burden to achieve the goal (İbn Manzur, Lisan al-Arab; Edward William Lane, An Arabic-English Lexicon, Article J-H-D). In other words, jihad means the struggle to be fulfilled with knowledge, property, tongue and body for the sake of Allah.
Jihad has nothing to do with war, death or killing. Because the words haarb حرب and qitaal قتال are used for warfare in the Quran. For example: Allah ordered the Messenger, to make jihad with the hypocrites (al-Tahrim  9; al-Tawba  73). But the Messenger of Allah, did not know who the hypocrites were (al-Tawba  101). It would not be possible for him to fight an enemy he did not know. Therefore, jihad is something other than war. With jihad, he can try to prevent the harm of hypocrites. So jihad is all about struggle.
Jihad against disbelievers, should be based on the information given by the Quran, which is the Furqaan: “…Entry into a great jihad with him (Furqan).” (al-Furqan  52). Jihad must be done with the goods, with the body. But jihad with knowledge, is the greatest jihad.
Therefore, jihad means, all kinds of struggle and efforts, for the best way to explain oneness (tawheed) to humanity and to live it.