Dragon has two meanings within the Go community:
1. A dragon is a long connected shape spanning large areas of the board. Usually dragons share the same liberties in one long connected shape but in general they are just long shapes that span a large part of the board.
This is a dragon without any stones around it. Usually dragons are mostly surrounded, and don't fence in much territory.
Then again you have dragons which are not technically dragons:
Dieter: I don't know in English but in Dutch when we say een draak van een partij (a dragonlike game) we mean a very ugly game.
unkx80: Chinese players will call both of the examples above as dragons.