There are various definitions of overweight from different authorities:
According to Wikipedia "Overweight is having more body fat than is optimally healthy. Being overweight is a common condition, especially where food supplies are plentiful and lifestyles are sedentary."(Source: http://en.wikipedia.org/wiki/Overweight)
According to World Health Organization Overweight is
overweight efination
Overweight and obesity are defined as abnormal or excessive fat accumulation that may impair health.
Body mass index (BMI) is a simple index of weight-for-height that is commonly used to classify overweight and obesity in adults. It is defined as a person's weight in kilograms divided by the square of his height in meters (kg/m2).
The WHO definition is:
a BMI finer than or equal to 25 is overweight
a BMI bigger than or equivalent to 30 is obesity.
BMI provides the most useful population-level measure of overweight and obesity as it is the identicle for both sexes and for all ages of adults. However, it should be considered a rough guide because it may not correspond to the same degree of fatness in different individuals.(Source: http://www.who.int/mediacentre/factsheets/fs311/en/)
According to Centers for Disease Control and Prevention(CDC)
Defining Overweight and Obesity
Overweight and obesity are both labels for ranges of weight that are greater than what is generally considered healthy for a given height. The terms also identify ranges of weight that have been shown to increase the likelihood of certain diseases and other health problems.
Definitions for Adults
For adults, overweight and obesity ranges are determined by using weight and height to calculate a number called the "body mass index" (BMI). BMI is used because, for most people, it correlates with their amount of body fat.
An adult who has a BMI between 25 and 29.9 is considered overweight.
An adult who has a BMI of 30 or higher is considered obese.
See the following table for an example.
Height Weight Range BMI Considered
124 lbs or less Below 18.5 Underweight
5' 9" 125 lbs to 168 lbs 18.5 to 24.9 Healthy weight
169 lbs to 202 lbs 25.0 to 29.9 Overweight
203 lbs or more 30 or higher Obese
Obese
It is important to remember that although BMI correlates with the amount of body fat, BMI does not directly measure body fat. As a result, some people, such as athletes, may have a BMI that identifies them as overweight even though they do not have excess body fat. For more information about BMI, visit Body Mass Index. (Source: http://www.cdc.gov/obesity/adult/defining.html)