One of first elements that we need to configure to execute a load test is the 'Thread Group'. These threads are created with Thread Group element. Each thread that executes the test plan is completely independent of other test threads. Multiple threads can used to simulate concurrent connections to the target server.
Using Thread Group, we can control the number of users Simulated (Number of threads), the ramp up time (how long it takes to start all the threads), and the number of times to perform the test.
JMeter thread group overview: