Precisely what is considered the distinction between "multithreading" and "massively parallel"?

In computer-programming:
What's the distinction between both of these principles? I'd often thought these to be interchangeable, however I discover this isn't really correct.

Multithreading:
Is all about an OS or an app managing several processes simultaneously. Basically threading is dividing cpu time between several tasks. Regardless if 1 or several CPUs are operating.

Massively parallel:
Describes CPUs. Parallel processing suggests that there's multiple processors within the computer. Massively parallel indicates there are numerous processors in the computer. If the OS is made to reap the benefits of parallel processors it then should disperse threads for any of multiple CPU cores.
Therefore multithreading is concerning precisely how applications handles multiple processes regardless of the number of CPUs there is in a given system. Massively parallel indicates the amount of Processors within the computer. By the way, distributed processing identifies just how the applications handle multiple Processors.