When light or sound waves bend as they pass obstacles, they diffract. Need proof that sound waves diffract? Just call out to your friend while you stand behind a big tree!
If you take a physics class, you'll learn about energy that travels in waves, including sound, light, and water. These waves move, spreading out after they pass through small openings and bending around the objects in their path. In other words, they diffract. Sometimes on a foggy night you can see the moon's light diffract around water particles in the air, forming a bright, glowing ring.