abdominals
Meaning
of Abdominal
Source: Webster's dictionaryExamples
A standard sidekick is performed by first chambering the kicking leg diagonally across the body, then extending the leg in a linear fashion toward the target, while flexing the abdominals.
Then afterward, or second in priority, focus on the smaller muscles, such as the biceps, triceps, calves, and abdominals.
The solution to that problem involves tightening the core (abdominals and back muscles).
Building core muscle will strengthen your abdominals, but it won't eliminate your belly fat, and might even make your belly look bigger as you're building the muscles.
Most have either visible abdominal muscle separation, or barely obscured, yet still firm, abdominals.