Generally speaking, a fakir or faqir (from Arabic) is simply an ascetic, hermit, or renunciate, of which there are many varieties. Yet the term fakir has been narrowed to refer primarily to thoe who performs acts of endurance or the seemingly impossible (such as holding their arm upright for many years), apparantly in an effort to strengthen their willpower.
"Asian fakirs fight in a frightful way within themselves in order to develop the force of willpower. The entire fakir’s path consists of multiple, incredible, and difficult physical practices. Any fakir is very capable of adopting any difficult physical position while keeping his body steady for hours, months, and even years; or he can sit under a tree on top of an anthill or under the scorching rays of the tropical sun. Any fakir is very capable of sitting on a bare stone under the sun with his arms opened in the form of a cross, or amongst thorns and caltrops for entire months or years. Indeed, fakirs develop the force of willpower in a severe way by means of all of these physical tortures. Nevertheless, they do not achieve the creation of the body of conscious will (causal body) because this is a one hundred percent sexual problem. If the body of conscious will (causal body) could be built with the physical tortures of fakirs, then according to the law of correspondences and analogies and in obedience to the hermetic maxim that states, “As above so below,” we would also have to state that the body of bones and flesh, the physi- cal body, can also be built with such practices. Consequently, the sexual act of father and mother would be superseded. Therefore, to affirm such an absurdity would be the lamenta- ble consequence of a mistaken idea." —Samael Aun Weor, The Narrow Way
"To obtain conscious will is impossible without working in the Ninth Sphere (Yesod, sex). Many places exist where people are submitted to tremendous tortures in order to acquire conscious will, but really they only store some energy. The true fakir has his guru and he does not leave India. The fakirs acquire many powers but nothing else. Some of them raise an arm and they do not lower it ever again. The arm becomes withered. They pursue willpower with such actions, but their willpower does not pass beyond such action. They do not achieve the building of the body of conscious will. All of this miraculous stuff deviates people; therefore, the fakirs are deviated." —Samael Aun Weor, Tarot and Kabbalah