Generally refers to computer memory that does not lose its stored data when power is removed. The exact criteria that makes memory non-volatile is somewhat ambiguous. Many manufacturers place standard (volatile) memory chips on a board with a battery and call it non-volatile. This is pretty widely accepted since the important thing is for the memory to hold its data while the device it is working in doesn’t have power. There are other types of memory that truly do not require power to hold their data. These include EPROMS, Flash, and obviously Read Only Memory (ROM). There are many other types.