These are usually procedural memories that occur secondarily to performing some other task. Implicit memory is highly adaptive, allowing us to acquire motor and spatial skills with little to no conscious effort. Explicit memory is more conscious, formal and deliberate. Implicit recall can occur even if explicit recall fails. Retrospective and Prospective distinctions in memory are important, especially after brain injury.
Retrospective memory involves the retrieval of past events.
Prospective memory involves remembering to do something in the future, or recalling one's plans and intentions. These include things like turning off the stove, taking medications, or showing up for an appointment. As with all analogies, you won't find a perfect match, but re-working this information into a more concrete model can help solidify your learning. Be careful though not to confuse this model with the real thing, or to think about memory in concrete terms. By Saturday midnight, make at least 2 substantive replies to others' remarks.