According to Aristotle in On the Soul, memory is the ability to hold a perceived experience in the mind and to distinguish between the internal "appearance" and an occurrence in the past.
ɐkˈoːɹdɪŋ tʊ ˈæɹɪstˌɑːɾəl ɪn ɔnðə sˈoʊl, mˈɛmɚɹi ɪz ðɪ ɐbˈɪləɾi tə hˈoʊld ɐ pɚsˈiːvd ɛkspˈiəɹɪəns ɪnðə mˈaɪnd ænd tə dɪstˈɪŋɡwɪʃ bᵻtwˌiːn ðɪ ɪntˈɜːnəl "ɐpˈɪɹəns" ænd ɐn əkˈɜːɹəns ɪnðə pˈæst.