Subconscious vs Unconscious
The confusion originates from Sigmund Freud who initialized the field with his idea of the unconscious mind. Freud was of course Austrian, and used the terms das Unbewusste and das Vorbewusste. These are  most accurately translated to unconscious and preconscious. The latter is the technical term for what you called 'subconscious'.

The word 'subconscious' is usually frowned upon in academic settings (because it is often unclear if it is talking about the unconscious or the preconscious). However, it is very popular in the everyday lexicon and thus creeps into scientific writing as well.

You can introduce further distinctions (such as subliminal) and if you want a nice and thorough modern treatment of all three terms in the context of visual processing, then I recommend:

Dehaenea, S., Changeux, J.-P., Naccachea, L., Sackura, J., and Sergent, C. (2006) "Conscious, preconscious, and subliminal processing: a testable taxonomy" Trends in Cognitive Sciences 10(5): 204-211. (pdf)