The short answer
Everyone has abdominal muscles; to see them you need low enough body fat and abs developed enough to show. Ab exercises alone do not burn belly fat; a calorie deficit does. Combine a moderate deficit, a high protein intake, regular strength training and two or three ab sessions a week.
Fat loss first
Abs show when little fat covers them. Vispute and colleagues (2011) found that six weeks of ab exercises did not reduce belly fat. A calorie deficit kept over time is the only way to lose it.
What body fat level?
It varies a lot from one person to another. Abs often start to show around 10 to 15 % body fat for men and 18 to 23 % for women, and some people lose belly fat last. Use photos and the mirror rather than chasing an exact number.
Build the muscle too
Thicker abs show through more fat. Train them like any other muscle, with loaded crunches, leg raises and rollouts, and make them progress. The ab workout guide gives the exercises and two circuits.
How long does it take?
At 0.5 to 1 % of body weight per week, losing 5 to 8 kg of fat takes several months. It is slow, and that is normal.
Keeping them
Very low body fat is hard to hold all year. Many people accept slightly less defined abs most of the time in exchange for more energy and better performance.
Put it into practice
About this guide
STARK editorial guide. Examples explain how to use the library and record training; they are not individual coaching.
Training principles: Vispute et al. (2011), Journal of Strength and Conditioning Research.
The session examples come from the STARK program catalogue linked above.