A thread can be defined as a sequence of instructions that can be run by a scheduler, which is that part of the operating system that decides which chunk of work will receive the necessary resources to be carried out. Typically, a thread lives within a process. A process can be defined as an instance of a computer program that is being executed.

In previous chapters, we have run our own modules and scripts with commands similar to $ python my_script.py. What happens when a command like that is run, is that a Python process is created. Within it, a main thread of execution is spawned. The instructions in the script are what will be run within that thread.

This is just one way of working though, and Python can actually use more than one thread within the same process, and can even spawn multiple processes. Unsurprisingly, these branches of computer science are called multithreading and multiprocessing.

In order to understand the difference, let's take a moment to explore threads and processes in slightly more depth.