Jmeter thread execution internal process?

when i ran jmeter script , i can see the below logs: Why it is repeatedly printed thread group 1-1,1-1,1-1...1-2 ?? I understood that 1-1 means first thread group - first thread but it is printed again and again what does that mean in execution side??

2014/11/27 03:45:59 INFO - jmeter.threads.JMeterThread: Thread started: Thread Group 1-1 2014/11/27 03:46:00 INFO - jmeter.threads.JMeterThread: Thread started: Thread Group 1-1 2014/11/27 03:46:02 INFO - jmeter.threads.JMeterThread: Thread started: Thread Group 1-1 2014/11/27 03:46:03 INFO - jmeter.threads.JMeterThread: Thread started: Thread Group 1-1 2014/11/27 03:46:05 INFO - jmeter.threads.JMeterThread: Thread started: Thread Group 1-1 2014/11/27 03:46:06 INFO - jmeter.threads.JMeterThread: Thread started: Thread Group 1-2 2014/11/27 03:46:08 INFO - jmeter.threads.JMeterThread: Thread started: Thread Group 1-2 2014/11/27 03:46:09 INFO - jmeter.threads.JMeterThread: Thread started: Thread Group 1-2 2014/11/27 03:46:11 INFO - jmeter.threads.JMeterThread: Thread started: Thread Group 1-2 2014/11/27 03:46:12 INFO - jmeter.threads.JMeterThread: Thread started: Thread Group 1-2 2014/11/27 03:46:14 INFO - jmeter.threads.JMeterThread: Thread started: Thread Group 1-3 jmeter.threads.JMeterThread: Thread finished: Thread Group 1-3 2014/11/27 03:47:51 INFO - jmeter.threads.JMeterThread: Thread finished: Thread Group 1-3

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