BMR

The basal metabolic rate - or about the number of calories your body would consume if you were living the non moving vegetable life.

For men and women in imperial “freedom” units this works out to:

$$\begin{array}{rl}\text{Male BMR}& =66+(6.2\ast \text{Pounds})+(12.7\ast \text{Inches})-(6.76\ast \text{YearsOld})\\ \text{Female BMR}& =655.1+(4.35\ast \text{Pounds})+(4.7\ast \text{Inches})-(4.7\ast \text{YearsOld})\end{array}$$

To get a better idea of what your actual daily caloric burn rate is so you can adjust your nutrition to maintain a healthy weight your BMR can be expanded upon by using your Total Daily Energy Expenditure multiplier or TDEE. The TDEE factors in the activity levels in your lifestyle to provide a better idea of where your caloric needs are.