[java] In a simple to understand explanation, what is Runnable in Java?

What is "runnable" in Java, in layman's terms? I am an AP programming student in high school, whose assignment is to do research, or seek out from others what "runnable" is (we are just getting into OOP, and haven't touched threads yet).

Runnable is an interface defined as so:

interface Runnable {
    public void run();
}

To make a class which uses it, just define the class as (public) class MyRunnable implements Runnable {

It can be used without even making a new Thread. It's basically your basic interface with a single method, run, that can be called.

If you make a new Thread with runnable as it's parameter, it will call the run method in a new Thread.

It should also be noted that Threads implement Runnable, and that is called when the new Thread is made (in the new thread). The default implementation just calls whatever Runnable you handed in the constructor, which is why you can just do new Thread(someRunnable) without overriding Thread's run method.