microSD is a format for removable flash memory cards. It is derived from SanDisk TransFlash and is used mainly in mobile telephones, but also in handheld GPS devices, portable audio players, video game consoles and expandable USB flash memory drives.
It is currently (2007) the smallest memory card available commercially. At 15mm × 11mm × 1mm (about the size of a fingernail), it is about a quarter the size of an SD card. There are adapters which allow a microSD card to be used in devices intended for SD, miniSD, or MemoryStick Duo cards, however they are not universally compatible.
TransFlash and microSD cards are the same (each can be used in devices made for the other), except that microSD devices can also support NFC (Near Field Communication).
As of November 2007, microSD cards are available in capacities from 64MB to 8GB. Cards at and beyond 4GB are available only in the newer SDHC format.