Multi-threading should just really be called “intelligent scheduling.” It’s making more efficient use of a CPU core by scheduling multiple different lines of code to run on a core at the same time. Some bits of code take longer to run then others and don’t make full use of the CPU during the time they run, so the CPU will schedule another thread/code snippet to run in that gap of downtime.
I’m certain someone will correct me and add clarity to this explanation, of course.