What does "unconscious memory" mean? Is there a single notion in the cognitive sciences for "unconscious memory"? For example a in a 2015 Northwestern University press release, we find that 


  
  Scientists retrieve unconscious memories
  Could lead to new treatment for patients with repressed traumatic memories 
  


So this is basically talking about repressed memories (in humans, as the motivation) and also state-dependent memory, as what they actually studied in mice.

On the other hand, in a different area of research we hear that


  The brain’s unconscious memories of patterns are likely to be partly responsible for some children struggling to learn to talk. 


Is this the same notion as any of the previous two? Looking briefly at the paper it seems like it's talking about procedural memory instead (correct me if I'm wrong).

So how many (sufficiently) different notions of "unconscious memory" are there in the (contemporary) science literature?
Although we usually refer to memory to describe our ability to consciously remember past experiences, in neuroscience this term is also used to incorporate unconscious influences of our past on our current perceptions and actions.
In other words, sometimes/in some instances, we are not aware of the influences of our past on our way to remember things.


  These unconscious influences on our current behaviour depend on what
  has been called implicit memory or nondeclarative memory that
  can exist in individuals with damage to the hippocampal memory
  system (centre of declarative or explicit / conscious memory).


This example is often made: if you try to describe how you learned to drive a stick-shift car,it is likely that you wouldn't do a good job of consciously reconstructing the chain of sequences that allowed you to learn how to drive a stick-shift car... Nevertheless, your behaviour would be a clear indication of you training.

Memory is not a single entity but consists of multiple processes or systems



References:
Emotional memory across the lifespan Elizabeth A. Kensinger