Carry on luggage can include suitcases, duffels and garments bags stored in the overhead bin on an airplane as well as smaller bags that can fit under the airplane seat in front of you.
When airlines refer to your “carry-on bag,” they are likely referring to smaller suitcases, duffel bags and weekenders that will fit in the overhead bin space, whereas “personal items,” in airline industry terminology, are bags small enough to fit under the seat, like travel totes and purses, laptop bags, diaper bags and briefcases or backpacks.
The most popular types of carry-on suitcases are spinners and Rollaboard bags. The exact dimensions of these bags vary, but all commercial airlines that allow carry-on luggage publish their size restrictions online. If you are unsure whether your bag qualifies, check the airline’s website for specifics.