A microSD card is a format for removable flash memory cards.
The cards are commonly used in mobile phones, as well as in some newer handheld GPS devices, portable media players, digital audio players.
The removability of the memory card makes it so you can take the information you have on one card and use it in another digital interface.
microSD cards are currently available up to a capacity of 32GB. These are know as SDHC (SD High Capacity) cards.