Gas limit is an amount of ethereum and it is multiplied by a very small amount of ethereum to pay people to record transactions and do other software actions. If the amount of gas is insufficent to complete the work, the work will fail. On the other hand, you can pay a bit more gas and expect the computers to complete your task sooner.
Gas is calculated by multiplying a very small amount of ethereum, known as “gwei” and “gas price”, and multiplying that by how much you want to spend, known as the “gas limit”. Gas limit is calculated in large numbers, think tens of thousands. The average gas limit for sending ethereum is 21,000. Because some software actions may require a larger gas limit, you need to be sure you include a large enough gas limit or your task will fail.