Everyone's abdominal wall is made up of five different muscles that run from the ribs to the pelvis. The top layer, known as the rectus abdominis, is the longest muscle of the abdominal wall and is comprised of three fibrous bands that run vertically up the abdomen. Several fibrous tissues known as tendinous intersections run horizontally across the center vertical band, cutting the abdominal wall into sections, which eventually can give way to the appearance of six-pack abs.

The number of tendinous intersections you have indicates how many abs you show. This number is determined by genetics. Around 60% of the population is born with three tendinous intersections, which means most people would sport six-pack abs if they worked at it, according to multiple studies. Approximately 20% instead have four of these intersections, which make up eight distinctive abs. In rarer cases, a person may have fewer abs: about 15% of people max out at a four-pack and around 2% top out at a two-pack.

The number of abs you have has nothing to do with how strong your core is. Having an eight pack doesn't necessarily mean you have superior abs or stronger abs than somebody who was born with three of those tendinous intersections, where there are six sections. Some people just have more sections than others.