What is the name of a circuit that generates a signal at a specific frequency?

An oscillator is an electronic circuit designed to produce a continuous, repeating waveform without any external input signal. In radio applications, oscillators provide the fundamental carrier wave or tuning frequency needed to transmit or receive signals. Reactance and phase modulators modify an existing signal to encode information, rather than generating the original base signal. Similarly, a low-pass filter allows low frequencies to pass while blocking higher ones; it modifies an existing signal but cannot generate a new one on its own.