Turnaround time is like how long it takes to finish something. For example, if you are waiting for someone to make you a sandwich, the turnaround time would be how long it takes for them to make the sandwich and give it to you.
Turnaround time is important in many different places, like in a store. If a store promises to have your order ready in 30 minutes, the turnaround time is 30 minutes. That means you should be able to come back in 30 minutes and your order will be ready for you.
Turnaround time can also be important if you are sick and need a test done. If you go to the doctor and they take a sample of your blood, it might take a few days to get the results back. The turnaround time would be how long it takes to get the results back from the test.
Overall, turnaround time is just a measure of how long it takes to finish something. It can be important to know, because you might have to wait for something or make sure you have enough time to finish a task before a deadline.