What is ERP (Effective Radiated Power)?

Effective radiated power (ERP) is an IEEE normalized definition of directional radio frequency (RF) power, for example, that is radiated by a radio transmitter. ERP is utilized in electronics and telecommunications, especially in communicating to quantify the apparent power of a broadcasting station. ERP estimates the combination of the power radiated by the transmitter and the direct power capacity of the antenna in a given direction. It is equivalent to the input power to the antenna multiplied by the gain of the antenna.