Gas is the fuel of Ethereum. It's not ether - it's a separate virtual currency with its own exchange rate.
Ethereum uses gas to control the amount of resources that a transaction can use (computation, memory, and storage), processed on thousands of computers around the world.
The gasPrice field in a transaction allows the originator to set the price they are willing to pay in exchange for gas.
Wallets can adjust the gasPrice in txs they originate to achieve faster confirmation. The higher the gasPrice, the faster the transaction is likely to be confirmed.
