Flash Memory is digital electronic memory that is non-volatile - that is it keeps its contents without the need for power - and can be written to and read from many times. This means that digital photos can be stored in flash memory, and will not be lost when the camera has no battery; also the photos can be deleted and the memory space reused for further photos.
Flash memory is used as the storage medium in most digital cameras - but is also used for may other purposes, such as mobile phone internal and SIM-card storage and firmware on computer motherboards or embedded devices such as set-top boxes. Many small laptop and palmtop computers rely on flash memory in place of hard disk drives.
For photographic use, it is normally formatted and accessed as a disk drive. This makes it simple to transfer whole cards to a computer - which then needs no extra software to read the card. Cards can be connected via the camera itself, or a card reader. Some computers have built-in card readers, but these are readily-available as USB devices for almost any computer.
Some flash-equipped cameras have some or all of their memory built-in and fixed, whilst others have removable "cards", allowing the photographer to simply change the card when the memory is full and continue taking pictures.
There are numerous types of flash memory card, some of them (more-or-less) open standards, and some proprietary - such as