What is Gas
Gas is a unit of measure that is primarily used to calculate the amount of work required in a contract transaction.
It is generally paid to the miner/verifier as a reward fee.
The higher the Gas fee given, the faster that transaction will be.
A certain amount of Gas is consumed for each transaction to avoid people making too many invalid transactions on top of the blockchain.
PS: Transaction Fee Calculation: Transaction Fee = Gas Usage x Gas Price
Gas Price: The price of Gas is calculated in Gwei, which is a very small unit of Ether (ETH) (1 Gwei = 10-9ETH). Users will need to set the price of Gas they are willing to pay for each unit of Gas when sending a transaction.
Gas Used: The amount of Gas that is actually consumed after a trade is executed is called Gas Used. The final transaction cost is the Gas Used multiplied by the Gas Price.
Gas Limit: Users also need to set a Gas Limit when sending a trade, which is the maximum amount of Gas they are willing to pay for the trade. If the amount of Gas needed to execute the deal exceeds this limit, the deal will fail (but the Gas cost will still be partially deducted).