Learn in the textbookBasics of Semiconductor Memory — RAM, ROM, and Volatility
DefinitionFlash memory (フラッシュメモリ) is non-volatile semiconductor memory that can be rewritten electrically and keeps its contents when the power is off.
ExplanationData is erased in fixed units (blocks) before being rewritten. It is widely used in portable storage media and in storage devices that replace hard disks.
AnalogyIt is like a notebook written in pencil. You can erase and rewrite many times, and the writing stays when you close it, but erasing too often wears the paper down.
Memory hookIt is said to be named for the way it erases a whole block at once, in an instant like a camera flash.