A lot of people confuse abs and core. Core is hips and lower back muscle, abs and glutes. To train this means no injuries, more stamina, soothing pain and better posture.
Here you can see the best 3 day plan to melt the fat.
Here are 3 workouts and just done in 5 min so do them at home. Also do them twice if you can. Skyscrapers 10 each side, windshield wiper 10 each side, army crawls 36 steps.
Here you can do 4 moves and repeat each set again. Breakdancer 15 per side, skydiver 30 seconds, dead bug 10 reps and threading needle 10 per side.
These are hard and need 6 min circuits. Crab kick to superman 6 for side, star leg raise 10 per side, side V up 10 per side and under/over 10 per side.