Anamnesis (= "recollection, reminiscence") is a term used in medicine, philosophy, psychoanalysis and religion.
In other words, if you don't know any of the attributes, properties, and/or other descriptive markers of any kind that help signify what something is (physical or otherwise), you won't recognize it, even if you actually come across it. And, as consequence, if the converse is true, and you do know the attributes, properties and/or other descriptive markers of this thing, then you shouldn't need to seek it out at all. The result of this line of thinking is that, in either instance, there is no point trying to gain that "something"; in the case of Plato's aforementioned work, there is no point in seeking knowledge.
Socrates' response is to develop his theory of anamnesis. He suggests that the soul is immortal, and repeatedly incarnated; knowledge is actually in the soul from eternity (86b), but each time the soul is incarnated its knowledge is forgotten in the shock of birth. What one perceives to be learning, then, is actually the recovery of what one has forgotten. (Once it has been brought back it is true belief, to be turned into genuine knowledge by understanding.) And thus Socrates (and Plato) sees himself, not as a teacher, but as a midwife, aiding with the birth of knowledge that was already there in the student.
The theory is illustrated by Socrates asking a slave boy questions about geometry. At first the boy gives the wrong answer; when this is pointed out to him, he is puzzled, but by asking questions Socrates is able to help him to reach the true answer. This is intended to show that, as the boy wasn't told the answer, he could only have reached the truth by recollecting what he had already known but forgotten.
Secondly, he makes clear that genuine knowledge, as opposed to mere true belief, is distinguished by its content. One can only know eternal truths, for they are the only truths that can have been in the soul from eternity. Though it can be very useful to have a true belief about, say, the best way to get from London to Oxford, such a belief does not qualify as knowledge; how could the human soul have known for all eternity a fact about places that have existed for less than 2,000 years?
Porphyry's short work De Antro Nympharum (ostensibly a commentary on the brief passage in Odyssey 13) elucidated this notion, as did Macrobius's much longer Commentary on the Dream of Scipio. The idea of psychic memory was used by Neoplatonists to demonstrate the celestial and immaterial origins of the soul, and to explain how memories of the world-soul could be recalled by everyday human beings. As such, psychic recollection was intrinsically connected to the Platonic conception of the soul itself. Since the contents of individual "material" or physical memories were trivial, only the universal recollection of Forms, or divine objects, drew one closer to the immortal source of being.
Anamnesis is the closest that human minds can come to experiencing the freedom of the soul prior to its being encumbered by matter. The process of incarnation is described in Neoplatonism as a shock that causes the soul to forget its experiences (and often its divine origins as well).
For example, in the Divine Liturgy of Saint John Chrysostom, the anamnesis begins with the words:
In most western Christian traditions, on the other hand, the anamnesis comes after the epiklesis.
An Episcopal Dictionary of the Church says of the anamnesis: "This memorial prayer of remembrance recalls for the worshipping community past events in their tradition of faith that are formative for their identity and self-understanding" and makes particular mention of its place in "the various eucharistic prayers".