The subconscious was a term utitlized in Freudian theories whereas unconscious was popular among Jungians. The unconscious is a place for example...where the symbolisms for dream interpreting are held... and the conscious state while dreaming itself. The subconscious is basically not referred to in modern psychology theories since 1960's Germany. I recommend reading Jungs' "Man and His Symbols" for an outstanding investigation of the intertwinement of these terms.