Wikipedia
Nafs is an Arabic word ( cognate of the Hebrew word nefesh ) occurring in the Qur'an and means self, psyche ego or soul. In the Quran, the word is used in both the individualistic (e.g. verse 2:48) and collective sense (verse 4:1), indicating that although humanity is united in possessing the qualities of a "soul/nafs/consciousness" they are individually responsible for exercising the agencies of their "free will" that it provides them.
Much of the popular literature on nafs, however, is focused on the Sufi conceptions of the term. According to the Sufi philosophies, the nafs in its unrefined state, is "the ego", which they consider to be the lowest dimension of a person's inward existence, his animal and satanic nature. Nafs is an important concept in the Islamic tradition, especially within Sufism and the discipline of gnosis ( irfan) in Shia Islam.