The phrase jihād al-akbar (the greater jihād) refers to striving against the nafs (the lower self) due to its persistence in desires and pleasures, its insistence on continuing in them, and its being overtaken by acts of disobedience (māʿṣiyya, behaviors and attitudes characterized by rebellion against Allah). This is the meaning of the statement of Allah, the Mighty and Majestic. (Futūḥ, 143)
See also: jihat-i kubrā (the greatest direction) 179
When you wish to strive against your nafs, subject it to the rule of knowledge in every action, force it into khawf (fear) at every step, and wherever you may be, constrain it by the awareness of Allah.