Say you have:

  function one() {
    console.log("one");
    setTimeout(one, 1000);
  }
  
  function two() {
    console.log("two");
    setTimeout(two, 2000);
  }
  
  one();
  two();

They are executing concurrently, but never in parallel (since javascript is single threaded).

Now, how do you coordinate them if you need to? This is what CSP helps you do.