Spot reduction is simply the idea that if you work a specific muscle group you will decrease the amount of fat in that area. The most common example of this is people focus on abdominal exercises (men especially) in an effort to lose weight in their stomach area, or hips and buttocks exercises (especially women) to reduce weight in the lower body area.
Being realistic you will never attain a flat stomach or tighter bum or legs by just performing specific exercises for these body parts alone.
The reason is simple the muscle does not own the fat that covers it. Sit up’s and squats or lunges will definitely strength you’re abdominal or legs and butt, but it will not get rid of the fat.
To lose fat anywhere in your body you need to burn kilojoules, understanding your hormones also but eating healthy, and by reducing junk food as well as following a program of both weights and cardiovascular training.