Here are some quick solutions.

Stablecoins are a special type of token and by name, are quite self-explanatory, they are coins that are overall more stable. Unlike cryptocurrencies whose price fluctuates quite a lot due to various reasons, stable coins are coins whose value is pegged to some external reference. This could be a precious metal, fiat currency or crypto assets. More info here.
Gas is the internal pricing for executing a transaction or contract. More info here.