What is Thread
Thread is a light weight process runs with in an application or a process to perform or execute desired set of instructions. Every thread in an application execute part of the instructions with in the process, lets take an example of any application running in a computer.
For now let's take a video player running on a personal computer as example, in this case framing images is performed by a Single Thread and Playing Music or Audio will be performed by a different thread.
Playing Video with Audio is a process but framing images and playing audio is two different set of threads. For any process we can have more than one thread like a video player and runs with in its scope by communicating each thread with other threads.
Thread is different than the process, from the above example a video player is process and playing sound, framing the images are threads. But in this case there should be ample of communication for each thread is required otherwise Playing Video and Audio will not be in Sync.