What is oscilator?

If you need to make a sound wave, you can use a tuning fork, an iron bar, or a bell.
You give any of them some energy by hitting it with a hammer, and out comes a genuine
sound wave, with a frequency, a wavelength, a period, and an amplitude.

Or you can use a tightly stretched elastic substance, or an enclosed container of air,
like a guitar string, a rubber band, a vocal chord, a drum-head, an organ pipe, or an
empty soda bottle. You put some energy into it by plucking it or blowing air past it,
it vibrates, and it sets up a sound wave in the air around it.

What if you need a radio wave ? No problem there. We know how to use electronic
parts like capacitors, coils, vacuum tubes, or transistors to build circuits that you can
put energy into with a battery, and they'll set up vibrating current in a wire, and the
wire will radiate radio waves into space.

The circuit that makes vibrating currents when you put in energy is an oscillator.
If you need to make a sound wave, you can use a tuning fork, an iron bar, or a bell.
You give any of them some energy by hitting it with a hammer, and out comes a genuine
sound wave, with a frequency, a wavelength, a period, and an amplitude.

Or you can use a tightly stretched elastic substance, or an enclosed container of air,
like a guitar string, a rubber band, a vocal chord, a drum-head, an organ pipe, or an
empty soda bottle. You put some energy into it by plucking it or blowing air past it,
it vibrates, and it sets up a sound wave in the air around it.

What if you need a radio wave ? No problem there. We know how to use electronic
parts like capacitors, coils, vacuum tubes, or transistors to build circuits that you can
put energy into with a battery, and they'll set up vibrating current in a wire, and the
wire will radiate radio waves into space.

The circuit that makes vibrating currents when you put in energy is an oscillator.