Memories retained in the subconscious and that may be recalled using various techniques including word association, asking questions, dialogue, and "sleeping on it." Nothing is truly forgotten, but things may have been insignificant at the time, painful and so repressed, overshadowed by larger events, etc. Memories can be recovered if you know what you are looking for and if you know they are pertinent. Sometimes, events will remind you and otherwise tell you that something significant is missing.