In Discworld, there are two kinds of dragons: The swamp dragons (draco vulgaris), dragons as they have to appear as according to the rules of the nature, and the noble dragons (draco nobilis), the dragons as people have always imagined them.
The swamp dragons are nothing compared to the beasts of legends. They're small winged lizards, no longer than a few feet, and capable of breathing fire. They're sometimes kept as pets, but are not really very suitable for that - they're not particularly intelligent, they're difficult to keep, and are not very nice to look at for a long time.
They're omnivorous and able to digest everything (except metal, it seems), and turn that into material for flames. Inside these things is a very complicated chemical system; in fact, their digestive system, not designed very well, makes them extremely dangerous, because they have the tendency to explode at slightest miscalculation, biological blunder, or a mental problem. They're also subject to many, many different diseases. In fact, given their explosive nature, it is almost unbelieveable that many specimens are able to reach ages of several years.
The dragon breeders have their own terminology for different ages of dragons. A female swamp dragon is called a hen (up to third clutch) or a dam. A male swamp dragon is called a pewmet (up to 8 months), a cock (8-14 months), a snood (14-24 months) or a cobb (2 years to death). A group of swamp dragons is called a slump or an embarassment. A dead swamp dragon is called a crater.
Guards! Guards! by Terry Pratchett
The Discworld Companion by Terry Pratchett and Stephen Briggs