what is a corutine in unity code example

Example 1: c# coroutines

using UnityEngine;
using System.Collections;public class ExampleClass : MonoBehaviour
{
    IEnumerator WaitAndPrint()
    {
        // suspend execution for 5 seconds
        yield return new WaitForSeconds(5);
        print("WaitAndPrint " + Time.time);
    }    IEnumerator Start()
    {
        print("Starting " + Time.time);        // Start function WaitAndPrint as a coroutine
        yield return StartCoroutine("WaitAndPrint");
        print("Done " + Time.time);
    }
}

Example 2: c# unity coroutine

IEnumerator Fade() 
{
    for (float ft = 1f; ft >= 0; ft -= 0.1f) 
    {
        Color c = renderer.material.color;
        c.a = ft;
        renderer.material.color = c;
        yield return new WaitForSeconds(.1f);
    }
}