Flash memory is any hard memory (chip) that can be erased and written to and retains the information when not powered.
Things that are termed flash memory can inclued, USB Memory Sticks, Memory cards for phones cameras etc.
The old term for it is EPROM Erasable Programmable Memory, commonly used in all computers to hold the BIOS information. This BIOS could be FLASHED to update it. Hence the common term now Flash Memory.