electrically erasable programmable ROM
With normal ROMs you have to replace the chip (or chips) when new BIOS instructions are introduced. With EEPROMs, a program tells the chip's controller to give it electronic amnesia and then downloads the new BIOS code into it. This means a manufacturer can easily distribute BIOS updates on floppy, for instance. This feature is also called flash BIOS, and you might also come across it in devices like modems and graphics/video cards.