The document discusses different types of oscillators. It begins by defining an oscillator as an electronic circuit that generates a periodic waveform without an external signal, using feedback to convert DC to AC. It then provides examples of oscillator applications and describes different oscillator types including RC oscillators like the Wien bridge and phase-shift oscillators, and LC oscillators. The document focuses on explaining the working principles of the Wien bridge and phase-shift RC oscillators, deriving equations for their oscillation frequencies.