(Please excuse the length of this definition, but I enjoy being thorough.)
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...
Metallic (Good) Dragons
Gold: Looks much like a cross between a western and eastern dragon, breathes
fire, very wise. (Wings look like large fins.)
Silver: Traditional western dragon, with tall fin. Breathes frost, serene and graceful. (My favourite.)
Brass: Again a traditional western dragon. has connecting its limbs to its body, aquatic. Breathes lightning, fascinated with war. (Still good, though.)
Brass: Traditional western, has the fin-like wings of the goldy. Breathes fire, LOVES to talk.
Copper: Traditional western, fin-like wings. Spits acid. Incorrigable prankster.
Chromatic (EVIL!) dragons. (note all of them are traditionaly western.)
Red: Lives to destroy, incredibley greedy (even for a dragon.) Breathes fire (obviously).
Blue: Vain, proud, would do anything to save its hide. Breathes lightning.
Green: Manipulator, honey-tongued, curious of other creatures. Very interesting breath weapon, it spits a cloud of corrosive vapour. (My favourite chromey.)
Black: Horrible temper, territorial, cruel. Spits acid.
White: Very STUPID. Breathes frost. (More of an animal than a higher being.)
Note that these dragons are intelligent (except thew white), and cast magic, speak, manipulate, conquer, what have you. Most of the above stuff is from DD..