What is parallel execution in TestNG?
Parallel execution is one of the most useful aspects of the TestNG framework. It allows you to specify the number of threads that will be used to run your tests simultaneously. Parallel execution is particularly useful when you are running tests on a computer that has multiple CPUs, or when you want to run your tests in a faster way.
Learn more: https://www.tutorialspoint.com/testng/testng_parallelexecution.html