What is the difference between multithreading and multiprocessing ?

• Threads are lightweight compared to processes
• Threads share the same address space and therefore can share both data and code
• Context switching between threads is usually less expensive than between processes
• Cost of thread intercommunication is relatively low that that of process intercommunication
• Threads allow different tasks to be performed concurrently.

The typical difference is that threads (of the same process) run in a shared memory space, while processes run in separate memory spaces.
If we consider running a word processing program to be a process, then the auto-save and spell check features that occur in the background are different threads of that process which are all operating on the same data set (your document).