EPROM stands for Erasable Programmable Read-Only Memory. EPROM is an early form of flash memory chip that retains its data after the power supply has been terminated. The most common use for this type of memory chip is for storing computer BIOS (Basic Input Output System) that is used to bootstrap a computer's operating system. Another common use of this type of memory chip is in the development of video game cartridges. EPROMs contain a quartz window that allows for the erasure of the stored data. When the quartz window is exposed to ultraviolet light at a certain wavelength the chip is erased and can be reused. For this reason EPROMs usually have a sticker applied to cover up the quartz window and prevent unplanned erasure.
The life span of EPROM memory is uncertain. Some estimates are that properly stored EPROMs will last 10-30 years but there doesn't appear to be any conclusive scientific studies to back up this estimate. A small leasson in Bit Rot, by Blackjax is a good article describing the preservation challenges associated with this type of medium.
SULAIR's collections on the history of the microcomputer contain large amounts of EPROM memory. It is anticipated that SULAIR's Digital Forensics Lab will be upgraded in the near future to handle this type of computer memory.
An ST Microelectronics 256Kbit 32KB EPROM chip, photo by Bill Bertram