microSD - definition
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.
There is a wide range of memory card formats. MicroSD (SD stands for "Secure Digital") and M2 (memory Stick Micro) are the smallest at the current time. The microSD format was originally called TransFlash or T-Flash.