EEPROM stands for electrically erasable programmable read only memory. It is a secondary storage device that once written (programmed) can hold data even when the power is removed.
If you need more storage for your project, or you want to learn how to use EEPROM, then this module is designed for you. It supplies an extra 256k byte for your project. You only need simply wire them via I2C.
1 x AT24C256 256K Serial EEPROM Data Storage Module