Explain what is meant by thread joining in programming.

Thread joining in programming is an operation where one thread waits for the completion of another. For example, if you have a main thread and several additional threads, calling the join() method on an additional thread will cause the main thread to pause until that additional thread finishes.

In Python, it looks like this:

import threading

def worker():
    print("Thread has started working")

thread = threading.Thread(target=worker)
thread.start()
thread.join()  # Main thread waits for thread to finish
print("Thread has finished, continuing work")

Thus, thread joining allows synchronization of execution and guarantees that certain operations will not start until others have finished.