An EEPROM (also called an E2PROM) or Electronically Erasable Programmable Read-Only Memory, is a non-volatile storage chip used in computers and other devices to store small amounts of volatile (configuration) data. There are several types of EEPROM chips. RTL83xx switch controllers user 24cXX series of I2C EEPROM.
This chip comes in DIP8 or SOIC8 packages and can store 4Kbits (512 Bytes). This is more, than required for RTL83xx, but is oftenly used for storing additional data (i.e. VLAN-configuraton), that is used inderectly (by additional microcontroller). See here for details.