Discman is Sonys trademarked name for what is more commonly known as the portable CD Player. The name was an extension of their original personal music product, the WalkMan.
The first DiscMan (The D-50) was released in North America in Early 1986(Late 1984 in Japan), a lot earlier than most people think. I happen to have one of these original beauties, so I'll give the rundown for it:
First off, compared to todays players, it's is a brick. It's easily over 1.5 inches thick, though it's only about 5.5 inches square. Unlike modern players, the case is made of steel. A full metal jacket, as it were. That makes it very heavy, but very tough, though I've never dropped it to test it. And, at probably 5 pounds, it would break a tile floor if I did. It's a player that means business.
Another interesting note is that the original DiscMan is not, as you might think, portable in the sense we think of today. It has no place for batteries and as such must be plugged into a 6-volt power source to function. It would work in a car or at home, but it was never made to be taken jogging. And you wouldn't want to, either, because It has no shock protection and skips if you blow on it wrong.
However, It is still a marvel of size. It was cutting-edge technology and they managed to fit it into the size of a portable tape player. It would not be until 1989 that it's power consumption issues would be dealt with (in the D-88 Pocket DiscMan) and it would be able to run off batteries (with a 2-hour battery life).