(NVS, persistent storage, memory) A term describing a storage device whose contents are preserved when its power is off. Storage using magnetic media (e.g. magnetic disks, magnetic tape or bubble memory) is normally non-volatile by nature whereas semiconductor memories (static RAM and especially dynamic RAM) are normally volatile but can be made into non-volatile storage by having a (rechargable) battery permanently connected.
Dynamic RAM is particularly volatile since it looses its data, even if the power is still on, unless it is refreshed. An acoustic delay line is a (very old) example of a volatile storage device.
Other examples of non-volatile storage are EEPROM, CD-ROM, paper tape and punched cards.