Obesity is the state in which your body has too much body fat and is stored under the skin and it pretty much means you are fat and need to loose some wait, hate to be harsh but its the truth.
Obesity is a condition when somebody has more than 30% body fat for women (normal is 25%) and more than 23% for men (normal is 18-20%). Such people are treated obese.
Also, BMI (Body Mass Index) is a measure for obesity and overweight. It is calculated by formula:
BMI = weight (kg) / height2 (m2) = 703 * weight (lb) / height2 (in2)
If you have BMI > 30, this extra body weight is already abnormal and could be dangerous for your health.