Non-Volatile memory is persistent without the need for power. While some technologies may have a definite shelf life after which their contents are not guaranteed, those times are much longer than most people would want as a duty cycle. For example, magnetic tape could be considered to be a form of non-volatile memory, but the material itself will degrade over time, making its contents unreliable.
The main types of non-volatile memory in use today are ROM, OTP flash and disk.
Nonvolatile Memory Design: Magnetic, Resistive, and Phase Change