When we are talking about memory we are talking about how we store information we have gathered from our environment and encoding within the brain in order to recall it at a later date.
One of the classic models of how memory works and how we are able to recall information is the Multi Store Model of Memory which was developed by Atkinson and Shiffrin in the 1960's. This model tells us that the process of storing information goes through a series of "stores" or steps in which we must progress through in order to place information from our enviroment, through our sensory organs (visual, auditory, smell, taste, and touch) which then goes into short term memory. When we have rehearsal of the information we have processed we are able to store it into long term memory for later recall.
The Levels of Processing model of memory was developed in the 1970's by Craik and Lockhart as they did not believe in the Multi Store Model. Where Atkinson and Shiffrin differentiated between short term and long term memory and stated that information must go through the short term memory in order to become a long term memory in which we can recall past the 8 to 10 seconds after being exposed to the stimulus, Craik and Lockhart proposed that there is no difference between short term and long term memory. Instead they stated there were different levels in which we processed the information within our environment. Shallow processing results in short term recall of what we have observed. Deep processing is when we process the meaning behind what we are observing within our environment. The deeper the level of processing results in the ease of being able to recall the information later.