self-nature [［自性]］ ( svabhāva; jishō): The individual nature that all things maintain; their unchanging identities. Also, the notion that things or beings exist independently, separate from all others.
Among all the Buddha's teachings, those on the nature of the self are the hardest to understand, yet they are central to the spiritual beliefs. In fact, "fully perceiving the nature of the self" is one way to define enlightenment. The Five Skandhas
Various schools of Buddhism interpret the skandhas in somewhat different ways. Generally, the first skandha is our physical form. The second is made up of our feelings -- both emotional and physical -- and our senses -- seeing, hearing, tasting, touching, smelling.
The third skandha, perception, takes in most of what we call thinking -- conceptualization, cognition, reasoning. This also includes the recognition that occurs when an organ comes into contact with an object. Perception can be thought of as "that which identifies." The object perceived may be a physical object or a mental one, such as an idea.
The fourth skandha, mental formations, includes habits, prejudices, and predispositions. Our volition, or willfulness, is also part of the fourth skandha, as are attention, faith, conscientiousness, pride, desire, vindictiveness, and many other mental states both virtuous and not virtuous.
The fifth skandha, consciousness, is awareness of or sensitivity to an object, but without conceptualization. Once there is awareness, the third skandha might recognize the object and assign a concept-value to it, and the fourth skandha might react with desire or revulsion or some other mental formation.
What's most important to understand about the skandhas is that they are empty. They are not qualities that an individual possesses because there is no-self possessing them. This doctrine of no-self is called anatman or anatta.
On the surface, this appears to be a nihilistic teaching. But the Buddha taught that if we can see through the delusion of the small, individual self, we experience that which is not subject to birth and death.
Beyond this point, Theravada Buddhism and Mahayana Buddhism differ on how anatman is understood. In fact, more than anything else, it is the different understanding of self that defines and separates the two schools.