6-packs are the result of a lot body fat which allows the tendons that run over the rectus abdominis muscle to be seen. They are all one muscle (well, 2, one on each side of midline). Most people have 3 tendons running over the muscles hence can get a 6 pack.
A 10 pack is not physiologically possible. The rectus abdominus muscle anatomically has 8 segments. 99% of the time has 8 segments. Maybe 7 or 9 if you're unlucky, but these are rare genetic anatomical variants; never 10.
The visibility of these segmentations depends on your bodyfat level, how big the muscle bellies are i.e. how hypertrophied, and genetics of your muscle belly insertions. Some people's bottom 2 segments aren't particularly distinguished, making it look like 1 segment. 8 pack is a result of well defined bottom segments.
this is a guy called Joseph Rakich. You can see he's shredded as **** but doesn't have an 8 pack - poorly defined bottom segments, probably genetic.