The Free On-line Dictionary of Computing (30 December 2018):

multithreading
multithreaded

    Sharing a single CPU between multiple tasks (or
   "threads") in a way designed to minimise the time required to
   switch threads.  This is accomplished by sharing as much as
   possible of the program execution environment between the
   different threads so that very little state needs to be saved
   and restored when changing thread.

   Multithreading differs from multitasking in that threads
   share more of their environment with each other than do tasks
   under multitasking.  Threads may be distinguished only by the
   value of their program counters and stack pointers while
   sharing a single address space and set of global
   variables.  There is thus very little protection of one
   thread from another, in contrast to multitasking.

   Multithreading can thus be used for very fine-grain
   multitasking, at the level of a few instructions, and so can hide
   latency by keeping the processor busy after one thread issues a
   long-latency instruction on which subsequent instructions in that
   thread depend.

   A light-weight process is somewhere between a thread and a
   full process.

   TL0 is an example of a threaded machine language.
   Dataflow computation (E.g. Id and SISAL) is an extreme
   form of multithreading.

   (1997-12-23)