One way to think about memory Memory
The ability to process information that requires attention, storage, and retrieval. is to think about putting things in a box. You place them there (a process called registration), you keep them there (a process called retention) and you take them out when needed (a process called retrieval). What happens in 'everyday' (routine/healthy) misplacing objects is that the memory for where the item was placed in the first instance was never laid down - the problem is one of registration, because you weren't paying attention at the time. By contrast, in Alzheimer's disease Alzheimer's disease
A neurological disease that affects memory and behaviour. It is characterized by beta-amyloid plaques and neurofibrillary tangles in the brain. There is no known cause but genetics and lifestyle are thought to play a role., the problem is one of retention - the memory has gotten lost, and therefore can't be retrieved.

The reality is more complex, of course. However, here is one way in which that account of registration/retention/retrieval falls short. When we retrieve a memory, it is not as though it was sitting in the box intact. Instead, what happens is that we assemble the memory from many pieces of information in the brain. In this way, a better word than 'retrieval' might be 'reassembly'.