Forgetting is a term used to refer to loss of a memory. It may refer to the decay or overwriting of information which has been temporarily stored in short-term memory. In general use, however, forgetting is usually assumed to refer to loss of information from long-term memory.
The biological mechanism of forgetting is still not completely understood. An old view (based on Freudian psychology) held that everything that is experienced is stored somewhere in the mind, and can always be retrieved, either by conscious recollection or through techniques such as hypnosis. Today, many researchers believe that stored memories can actually become lost, either by decay or by being overwritten with new information.
Often, the failure to retrieve a memory reflects not "forgetting" or loss per se, but the fact that the memory was not well stored in the first place. Alternatively, forgetting may be a temporary failure of retrieval; in this case, the memory is temporarily unavailable, but may be accessible later.
However, memories also simply grow weaker with time; details fall away. Such forgetting is an important component of healthy memory: without some mechanism for selectivity, memory would soon become overwhelmed by the details of every piece of information ever experienced.
Rehearsal or periodic retrieval of a memory certainly helps to prevent or delay forgetting; important or meaningful information can survive for decades or even a lifetime with no appreciable loss of detail.
Further reading: D. Schacter (1996). Searching for Memory: The Brain, the Mind and the Past. New York: Basic Books.
by Catherine E. Myers. Copyright © 2006 Memory Loss and the Brain