What is nafs?
Hans-Wehr Arabic-English Dictionary:
نفس nafs f., pl. نفوس nufoos, انفس anfus soul; psyche; spirit, mind; life animate being, living creature, human being, person, individual (in this sense masc.) essence, nature; inclination,liking, appetite, desire; personal identity, self.
Imam Ghazali wrote:
Meaning of nafs: It has two meanings. First, it means the powers of anger and sexual appetite in a human being… and this is the usage mostly found among the people of tasawwuf [sufis], who take “nafs” as the comprehensive word for all the evil attributes of a person. That is why they say: one must certainly do battle with the ego and break it (la budda min mujahadat al-nafs wa kasriha), as is referred to in the hadith: A`da `aduwwuka nafsuka al-lati bayna janbayk, Your worst enemy is your nafs which lies between your flanks.
The second meaning of nafs is the soul, the human being in reality, his self and his person. However, it is described differently according to its different states. If it assumes calmness under command and has removed from itself the disturbance caused by the onslaught of passion, it is called “the satisfied soul” (al-nafs al-mutma’inna)… In its first meaning the nafs does not envisage its return to God because it has kept itself far from Him: such a nafs is from the party of shaytan. However, when it does not achieve calmness, yet sets itself against the love of passions and objects to it, it is called “the self-accusing soul” (al-nafs al-lawwama), because it rebukes its owner for his neglect in the worship of his master… If it gives up all protest and surrenders itself in total obedience to the call of passions and shaytan, it is named “the soul that enjoins evil” (al-nafs al-ammara bi al-su’)… which could be taken to refer to the ego in its first meaning.
Imam Abu Hamid al-Ghazali, Ihya `Ulum al-Din (The Revival of the Religious Sciences): “Kitab sharh `aja’ib al-qalb” (Book of the Explanation of the Mysteries of the Heart).