'Subliminal' is a word with similar meaning to 'subconscious', but while the subconscious is generally quite comprehensive, 'subliminal' refers to that narrow band of subconsciousness which is just below the threshold of normal consciousness.
It may come as a surprise, but neither psychology nor the psychic field (or related spiritual traditions) are leading the research into subliminal awareness: it is advertising and marketing. Whether it is how to make a direct sale, design an ad, or arrange the shelves in the supermarket, consciousness (or lack thereof) is being exploited for profitability.
A psychic has two basic ways of integrating consciousness and subconsciousness: one way is the riskier 'deep delving' into the essence of things, and the other is the step-by-step expansion of consciousness into the subliminal part of subconsciousness.
It is relatively easy for a psychic to learn and expand into the subliminal realm: just start with what you already know and go from there. Expand, zoom in, zoom out, analyze, integrate, go with the flow, test and construct - make one step at a time and soon enough you will be amazed how far you've come.
With each step one level of psychic knowledge is integrated and a new level of subliminal psychic possibilities revealed.