What is the use of Pthread_Join function in Operating system

include
pthread_t tid;
int ret;
int status;
/* waiting to join thread "tid" with status */
ret = pthread_join(tid, &status);
/* waiting to join thread "tid" without status */
ret = pthread_join(tid, NULL);


The pthread_join() function blocks the calling thread until the specified thread terminates. The specified thread must be in the current process and must not be detached. When status is not NULL, it points to a location that is set to the exit status of the terminated thread when pthread_join() returns successfully. Multiple threads cannot wait for the same thread to terminate. If they try to, one thread returns successfully and the others fail with an error of ESRCH. After pthread_join() returns, any stack storage associated with the thread can be reclaimed by the application.