The formula here is power, which is actually change in energy over time, which is a rate flow is equal to sigma, which is a constant and will be given to you admissitivity value A and T. T is the temperature of the object. A is the area of the face that's radiating the heat, and this is a value between zero and one. Now, where this value is one, that that simply means that the object is absorbing all the heat, is absorbing all the radiation, which means that it also releases all the radiation, okay? Now, a black body object is an object that has this value that equals one. Now, technically, such an object does not exist, and that's because if such an object did exist, it would not reflect any of the waves and would not reflect light waves, and so we would not be able to see it. It would be invisible to us.