EPROM

An EPROM (rarely EROM), or erasable programmable read-only memory, is a type of memory chip. Unlike a normal programmable read-only memory (PROM), this type of chip can have its information cleared and written again.
EPROMs are cleared by shining ultraviolet light on the clear opening on their top. Some EPROMs can be cleared using only electricity instead of needing ultraviolet light. These are called EEPROMs (standing for electrically erasable programmable read-only memory).