What is the gold pieces in dungeons and dragons?

Answer 1

They're the generic form of money used by default; to simplify financial matters, it's assumed that every country is on a bimetallic (actually multimetallic) standard, that all coins are the same size and weight (this is not physically realistic, but then we're talking about a game where magic works and dragons exist), and that the exchange rate for various metals is fixed. A DM who really wanted to could change this to some more realistic economy, but most don't bother.

The exact exchange rates vary slightly between editions. The first edition had:

1 platinum piece = 5 gold pieces

1 gold piece = 2 electrum pieces

1 electrum piece = 10 silver pieces

1 silver piece = 10 copper pieces

This is rather unnecessarily complicated, and I think later editions have dropped the electrum piece and devalued gold by a factor of two so that 1pp = 10gp, 1gp = 10sp, 1sp = 10 cp.

One advantage of the system is that it doesn't really matter that the chest of gold you just found in the dungeon is a thousand years old: a gold piece is a gold piece (there's no such thing as inflation in Dungeons and Dragons), and in most campaigns, since it's the gold content that really matters, shopkeepers are just as happy to take any gold coin of the standard weight, no matter where or when it was minted.