In the traditional sense, dragons were large reptilian creatures first thought of in the medieval time. (medieval in the eastern and western sense.) In western realsm, the dragon was a greedy, tyranical brute who ate damsels, demolished villages, and kept a huge treasure hoarde. Mostly portrayed as a generally lizard-like creature with many crests and horns, terribley sharp claws, large teeth, sometimes quills or fur, and almost always wings. (Different variants occured, such as the wingless two-legged Linwurm, and the scorpion-tailed wyvern.)They might've also had a lion's or dog's head.
In the eastern realms, dragons were beneficial and wise. They did of course keep their treasure hoardes, a dragon is nothing without his shinies. (They're very good eating.)They were snakelike, colourful, posessed deer-antlers, usually had a mane of fur or a crest of the stuff running down their back. They were awfully powerful beings, usually close to the gods, and lived in mountains, and sometimes in the ocean. I don't kinow much more...I'm pretty sure they could breathe scalding water instead of fire.
Nowadays, dragons are an icon. Anime' abuses them, fantasy novels use them, and D&D keeps them sacred. In DD, there are two main types of dragons, called true dragons(western variety).
Here's a list...
You have to slay a couple of dragons before you find your princess!
Matt: "Joe, you slay that dragon yet?"
Joe: "No dude, she wants to be my girlfriend!"
Hey, you want to go dragon slaying tonight?
No, I already slew one today and then threw her out!
People often like to roleplay these creatures online.