For Bion, the unconscious is experiential reality that hasn't been articulated. Indeed, the unconscious can never be fully articulated because it is multidimensional (has, in effect, more dimensions to it than we can simultaneously process with our rational minds). Articulation, therefore, is always a process of simplifying (indeed, oversimplifying for the sake of managing) that which is irreducibly complex.
LEARNING FROM EXPERIENCE taught me that the unconscious is the catchment system of experiential reality, and the work to be done is in the further interpretation -- the actually simplifying -- of memory, in order to make it manageable, and to reduce the feeling of "nameless dread" (as it were, by giving the dread a name and a social context and meaning).
The naming of the prior existing "nameless dread" is the social contextualisation of it, by giving it an objectively recognised form (in words) and/or intersubjectively recognised form (in the moment of the communication of it). The mother of the infant initially is the one who acts to "contain" or hold the inarticulate emotions of the child, and thus she gives social form and shape to them.
The goal of coming to maturity is to convert nameless dread into something that is socially meaningful. Thus the interpretive movement between the "paranoid-schizoid position" of disintegrated self and inarticulated experience towards the "depressive position" that permits social communication, at the price of losing one's unity with the whole.
The Bion paradigm is also shamanistic: the subject mediates between the multidimensional space of the unconscious field and everyday, limited three-dimensional reality, which can be articulated therefore can be expressed rationally.