Nice question Laura.
It’s good to understand the makeup of the rectus abdominus to understand why we see the “six pack.” The rectus abdominis is a paired muscle group made that separates the right rectus ab from the left rectus ab. Each vertical column is has three horizontal fibrous bands called tendinous inscriptions. So the six pack that you are seeing is the rectus abdomonis with very little adipose tissue surrounding it.
As mentioned with proper diet and exercise it is possible to have a six pack and if you have the right genes even an eight pack.