Post-Lacan, a lot of psychoanalytic thought, even that which would openly disown him, has come to involve three layers of reality that are interlinked, but to some degree independent of one another -- the real, the ideal and the symbolic. These reside in the material, mental and cultural realms, respectively. (They have deeper historical psychoanalytic roots in the notions of neurotic movement 'from', 'against' or 'toward' in Horney. But Lacan gave them independent footing and an entirely different use.)
There is a temptation on the part of dualists to re-tread back from Lacan into Jung and consider the symbolic to be unconscious ideal material. But that makes it very hard to consider how it can be both personal and collective in nature, or how it does not, in fact, lose its force when it is discussed consciously, in the way that classically repressed ideas should.
Symbolism is intersubjectively established, so it cannot exist without interaction within the material realm between people with differing mental contents. It needs a material cue, but it resides spread across minds, in a culture, so it cannot be collected up as a mental object. Without some spooky sort of Berkeleyan or Hegelian "Overmind of God", you need a third category of being to account for our human structure as social animals and our dependence upon cultural contents.
It is also tempting to discount it as unnecessary category representing a combination of the other two. But our new awareness of the depth of 'Sapir-Worf' effects, and the degree to which humans are dependent upon language for thought implies that thought is not logically prior to symbolization. If symbolization is prior to thought, then, so is material, and there is either one, or three things going on, right from the beginning not two out of which the third arises.
(This seems to be, at base, @JoWehler's answer. Except that Lacan's ideas are both earlier and deeper than Popper's more 'positivistic' sudivision.)