回忆(huí yì) - memory, recollection, to look back on in Mandarin

回忆 (huí yì) works both ways: as a noun it is a memory you hold, as a verb it is the deliberate act of casting your mind back. 美好的回忆 is a happy memory; 回忆起 is to call something to mind.

Its measure word is 段, 一段回忆, the same one used for a stretch of time or a length of road. That tells you how Chinese pictures it: a memory is a section of the past, not a single object.

Three related words trip learners up. 记得 (jì de) is simply to remember a fact, no effort involved. 记忆 (jì yì) is memory as a faculty, the thing that gets worse with age. 回忆 is the active looking back. Ask whether effort and nostalgia are involved, and if they are, 回忆 is your word.