The power that is lost in transmitting a signal from one point to another. In wireless technology, for example, transmission loss can occur when a signal passes through walls, ceilings, etc. Or it can simply occur over (and due to) distance. Wires also have transmission loss due to resistance, inductance and capacitance. Transmission loss can add up significantly over long distances so many times special equipment is required (such as repeaters, for one example) to maintain the desired integrity of the signal.