Learn in the textbookBasics of Semiconductor Memory — RAM, ROM, and Volatility
DefinitionNon-volatile memory (不揮発性メモリ) is memory that continues to retain its stored contents even after the power is turned off.
ExplanationBecause it needs no power to hold its contents, the same data is available after the power is turned back on. Among semiconductor memories, ROM and flash memory have this property.
AnalogyIt is like notes written in a notebook. Close it and put it in your bag, and the same notes are there the next time you open it.
Memory hookThe word adds the negating 不 ("not") in front of 揮発. Not flying off means staying, which the makeup of the word itself tells you.