MicroSD is a format for removable flash memory cards. It is derived from SanDisk TransFlash and is used mainly in mobile telephones but also other portable devices
This card to date (2008) is the smallest memory card available commercially. At 11†mm ◊ 15†mm ◊ 0.7†mm (about the size of a fingernail) There are adapters which allow a microSD card to be used in devices intended for SD, miniSD, MemoryStick Duo and even USB cards. However, they are not universally compatible.
All Micro SD cards above 2GB are known as Micro SDHC and the user must ensure these cards are suitable for their device.