According to Wikipedia, your basal metabolic rate (BMR) is the amount of energy expended while at rest in a neutrally temperate environment, in the post-absorptive state (meaning that the digestive system is inactive, which requires about twelve hours of fasting in humans). The release of energy in this state is sufficient only for the functioning of the vital organs, such as the heart, lungs, brain and the rest of the nervous system, liver, kidneys, sex organs, muscles and skin.

With that said it is also important to note that your BMR represents the largest (60% or more) portion of your daily caloric expenditure. Your BMR is about 1,200 to 1,400 calories daily for an individual whose total energy expenditure is 2,000 calories.