EPROM stands for Erasable Programmable Read Only Memory (Usually pronounced e-p-rom), EPROM is a special type of memory that retains its contents until it is exposed to ultraviolet light. The ultraviolet light clears its contents, making it possible to reprogram the memory. To write to and erase an EPROM, you need a special device called a PROM programmer or PROM burner.
An EPROM differs from a PROM in that a PROM can be written to only once and cannot be erased. EPROMs used to be used widely in personal computers, before the advent of EEPROM, because they enabled the manufacturer to change the contents of the PROM before the computer was actually shipped, (So, the BIOS revision could be updated, for exmaple). This means that bugs with a particular piece of onboard software can be adderess, and new versions of firmware installed shortly before delivery, or shipping.