Abs Roller Wheel/Abs wheel/

That’s an ab roller wheel (also commonly called an ab wheel, abdominal roller, or core roller).

It’s a popular piece of home/gym fitness equipment designed primarily for strengthening and toning your core muscles (especially the abs/rectus abdominis, obliques, and transverse abdominis), while also engaging your back, shoulders, arms, chest, and even legs to some extent when used in various exercises.