A memory card is a flash memory data storage device used in a wide range of digital devices such as mobile phones, digital cameras, PDAs, music players, etc. They are small, rugged and offer high re-record ability and power-free operation.
There is a wide range of memory card formats. MMC (which stands for "Multi Media Card") is one of the oldest formats and has been replaced by newer ones like SD, microSD and microSDHC. Physically, it's fully compatible with SD cards.