This is an SD card reader/writer module.  This SD card module can be used to read and write SD (Secure Digital) cards with your Arduino, PIC, AVR, or other microcontroller.  This module is perfect for adding storage space to your project.  These are used all the time for data logging storage in embedded applications.  You can also use them to store program preferences, configurations, or game data.  This module features an on board logic level conversion IC which makes this module compatible with 5v or 3.3v systems out of the box.  Interface with this module is very easily done over a standard SPI bus.