A signal amplifier is an electronic device that increases the strength of a signal, making it easier to transmit over long distances. It is commonly used in various applications, such as audio systems, telecommunications, and broadcasting, to enhance the quality and clarity of the transmitted information. These amplifiers work by taking a weak input signal and producing a stronger output signal without significantly altering the original information. They are essential in devices like radio transmitters, television sets, and cell phones, ensuring that users receive clear and reliable communication.