First they had just plain ROMs (read-only memory). OEMs (orginal equipment manufacturers) sent the information to the maker of the ROMs, who put the data/programs in them. In contrast to RAMs (random-access memory), the contents programmed into these devices remained there after power was removed.
Then came P(rogrammable)ROMs – ROMs received by the OEM, who could then program them once only with an electrical instrument.
Then came E(rasable)PROMs, which the OEM could erase with UV light and reprogram.
Next there were EPROMs that could be erased electrically and were called E(electrically)EPROMs.
Thereafter came flash EEPROMs. I had flashed out by then, so I kind of forget their claim to flame, but I think it revolves about very quick reprogrammability without an erase phase. I believe they are the most common at present.
I think there are some other types also these days.
Ordinary “memory” is, of course, RAM (random-access memory). Of course, all the kinds of ROM (read-only memory) are just as random-access as RAM, but RAM came before all of the above, and the name was used to distinguish it from other, earlier (but still used) types of “volatile” (contents lost when power removed) memory, such as the linear, two-port shift registers, sometimes called FIFOs (first-in-first-out), LIFOs (last-in-first-out), or shift registers with “parallel” outputs from certain or all register cells.
Ray, retired electronics engineer (Memories are made of this. . .but I forget why. Well, actually biological memory is different. It is content-controllable and follows what is known to date about natural-neural-network theory.)