Gold is the currency used within each Dicey Dungeons episode. You start each run with 0 gold, and gain 1 gold for each enemy you defeat within the Dungeon.
According to the Thief, the coins are solid gold.
There are a few ways to gain Gold:
Gold is mainly used to buy goods and services at Yolanda's shop, including equipment, health, equipment upgrades, and occasionally equipment removal.
Additionally, a piece of equipment from a late episode, Call For Backup Thief? (shown as Thief? in-game), allows you to spend 1 gold to get a random piece of equipment for the turn it's used.