what is self?

"The Self usually begins as a random stream of sensory material -- sounds, images, tactile sensations, scents, flavors, stimulate the nervous system and, through a series of neurochemical processes affect the brain forming first impressions an the brain tissue. The key aspect of it is its randomness, every one is exposed to a different mosaic of impressions and everyone's nervous system react to them differently due to infinite variations of the genetic material regulating functioning of each person's nervous system.

So these first random impressions constitute the mosaic-like core of one Self, one's core-identity, the first filter/screen controlling the precursors of mental (neurocognitive) functioning.

So, at it's foundation the self is not other that the external world imposing itself (IMPRINTING itself) on the brain, colonizing the innocent tissue by organizing it to respond with internal images, sounds, voices, etc.

In the second stage, there is the process of connecting that internal mosaic imprinted on the brain to others in the world. Child's survival in the give and take of social world depends on successful development means to interact with others. The main means is language which serves as the primary vehicle of articulating the self in the world and for the world. Without it the growing individual becomes a deviant labeled retarded, asocial , psychologically sick etc.

And we are not approaching it on the level of psychology of cognition, perception, representation or the inner workings of the psychoanalytic conscious/unconscious."

Source: MindIs.com (Website on Buddhist Psychology and other things)