The process, mostly completed within several hours but which can last for…

Concept: encoding a piece of information does not by itself make it permanent. A newly formed memory trace is at first labile, and consolidation is the post-encoding process that stabilises that trace into durable long-term storage. Psychologists describe it in two phases: synaptic (cellular) consolidation, a fast, protein-synthesis-dependent fixing of the trace at the synapse that is largely finished within the first minutes and hours after learning, and systems consolidation, a far slower reorganisation in which the hippocampus gradually hands the memory over to neocortical networks over months and years.

Applying this to the item:

1. The first marker in the stem, “mostly completed within several hours”, matches the synaptic phase, which fixes the trace at the synapse soon after learning.

2. The second marker, “can last for years”, matches systems consolidation, which keeps reorganising the trace long after the learning event.

3. The stated function, fixing information in long-term memory, is exactly the job of that post-encoding stabilisation process, so the term the stem is defining is consolidation.

Cross-check against the other terms offered:

• Repression is a psychoanalytic defence mechanism: anxiety-provoking material is kept out of conscious awareness. It concerns access to an existing memory, not the stabilisation of a new trace.

• Episodic memory is a content system inside long-term memory (personally experienced events with their time and place). It names a kind of stored memory, not the process that fixes it.

• Retroactive interference is forgetting caused by later learning disrupting an earlier memory. It weakens retention rather than establishing it.

Hence the process described, running from the first hours after learning to years afterwards, is consolidation.