Multithreading is the ability of a central processing unit (CPU) (or a single core in a multi-core processor) to run many threads of CODE at the same time, with the operating system supporting it. Multiprocessing is not the same as Multiprocessing. Threads in a multithreaded application share resources from a single or several cores, such as computational units, CPU caches, and the Translation Lookaside Buffer or TLB (A translation lookaside buffer or TLB is a memory cache that speeds up access to user memory. It is a component of the Memory MANAGEMENT Unit or MMU on the chip. The TLB, also known as an address translation cache, records recent virtual memory to physical memory TRANSLATIONS). Multithreading TRIES to increase the use of a single core by exploiting thread-level parallelism as well as instruction-level parallelism in multiprocessing systems with several full processing units in one or more cores. Because the two approaches are complementary, they are used together in practically all modern system architectures that INCLUDE multiple multithreading CPUs and multithreading cores. 

We can see that in the above image, one single process has two threads of execution that run on one processor.