"Oblique crunches" is a term used to describe an exercise that focuses on the muscles on the sides of your abdomen, known as the obliques. It involves bending or twisting your body to work out these muscles and strengthen your core. Full definition
If you master this stomach exercise and want a greater challenge try oblique crunches on a bosu ball with the feet up or bicycle crunches on the bosu ball with the feet up. (ab-core-and-stomach-exercises.com)
If you want to be creative you can do stability ball oblique crunches with cables to add even more resistance and challenge your oblique muscles. (ab-core-and-stomach-exercises.com)
When performing hanging oblique crunches, avoid swinging. (homefitnessguru.net)