They call these crunches because they crunch those donuts out of your stomach. They also get those abs stronger and more toned so you can show off your beach body without fear.
Start by laying down on your back with your knees bent. With your arms out in front of you, "crunch" up by bringing your shoulders up off the ground. Make sure you keep your back straight and abs tight and then bring yourself back down slowly. Repeat as many times as you can in 30 seconds.