Source : Free On-Line Dictionary of Computing

Erasable Programmable Read-Only Memory
     
         (EPROM) A type of storage device in which the data
        is determined by electrical charge stored in an isolated
        ("floating") {MOS} {transistor} {gate}.  The isolation is good
        enough to retain the charge almost indefinitely (more than ten
        years) without an external power supply.  The EPROM is
        programmed by "injecting" charge into the floating gate, using
        a technique based on the tunnel effect.  This requires higher
        voltage than in normal operation (usually 12V - 25V).  The
        floating gate can be discharged by applying ultraviolet light
        to the chip's surface through a quartz window in the package,
        erasing the memory contents and allowing the chip to be
        reprogrammed.
     
        (1995-04-22)