Jihad is one of the most misunderstood aspects of Islam, and in most cases is taken as holy war. Unlike crusades, Islam does not have the concept of holy war.
In Islam, fighting in a war can be Jihad if one is fighting only and only for the cause of God. Fighting for territorial gains, nationalism, pride, money or the community is not Jihad.
Islam allows Muslims to fight back against oppression or if they are attacked; but it will not be Jihad if they retaliate in revenge. Even under such circumstances God prefers those who forgive.Muslims are also required to fight for the protection and safety of people of other faith living under their rule.

Muhammad (Peace be upon him) had set unprecedented standards of humanity during wars. He forbade killing of the innocent, women, children, old and the sick, destruction of crops, cutting of trees and killing of livestock during wars.

The word Jihad is derived from the word Jehd, which means to struggle.
Muslims are required to wage Jihad for the cause of God to make this world a more livable place.The foremost Jihad is fighting against one’s own evil desires to stray from the right path, by obedience of God and His last Messenger Muhammad (Peace be upon him).
Acquiring knowledge, applying that in one’s life and passing that to Muslims and non-Muslims alike are some other forms of Jihad.
Jihad can also be waged by speech and prayers for guidance and not by spreading hatred.