The fee you pay the network for any on-chain action (transfers, trades, contract interactions) to cover the cost of computation and validation. It's usually paid in the chain's native token (for example, ETH on Ethereum), and its level floats with network congestion — the more people competing to get on-chain at once, the higher the gas fee.

Short for Total Value Locked, the total value of crypto assets currently deposited and locked in a DeFi protocol or a chain. It's a common metric for how much money is using it, often used as a reference for scale and popularity — but it fluctuates with token prices and can be artificially inflated, so it can't alone guarantee safety or value.