The part of Short-Term Memory in which things are organized by their meaning.
This is what most of us use most often; you see a banana, and rather than recording it in your short-term memory as a picture of a banana, you store it as an abstract concept. Later, you will likely be able to recall that you saw a banana, but you will probably not remember distinctive features of the banana (number of spots, size, degree of curve) unless they were rather startling to you at the time. If you do remember these things (assuming that you were not specifically trying to remember them), you probably did code it visually rather than semantically, and you may be in possession of a photographic memory (high levels of visual coding).
This type of coding is in evidence in the phenomenon of proactive inhibition: when learning new stuff, 'like meanings' will interfere with each other, while 'unlike meanings' will not (as much). This is to say, learning something new about dogs (for example) may be made more difficult because of older information you know about dogs, but this old dog information will not hamper your learning new information about bananas. The key here is that it is the actual meanings, and not the visual or acoustic representations, that are being remembered.
If given the list of words 'lawyer', 'doctor', and 'teacher', you will then have more trouble remembering the word 'minister' than the word 'banana'. 'Minister' tends to get lumped in the 'professions' category and lost, while 'banana' is off in it's own category, well separated, semantically, from the list of words you had been given earlier.
The other parts of short-term memory are Acoustic code and Visual Code.