Just about any device that produces a back-and-forth or up-and-down motion—particularly if that motion is shaped like a sine wave--can be called an oscillator. One of the simplest examples is a pendulum; if the path of a pendulum were charted on a graph, that path would approximate a sine wave. The same is true of a suspended spring.

In electronics, an oscillator is a circuit that generates a pulsed, or periodic, signal. These signals can also resemble sine waves, though some generate square or saw-toothed pulses. Oscillators that produce sine waves are called sinusoidal, while the remainder are called non-sinusoidal.

Sinusoidal quartz oscillators are widely used as signal amplifiers. They can be found as integral parts of radios, radar systems, and just about every other electronic communication device. Because of the regularity of the pulses they generate, both sinusoidal and non-sinusoidal oscillators are used as timing devices. Such timers are used in televisions and digital computers.

Perhaps the most advanced oscillators are the maser and the laser. During the 1940s the oscillator had become an important tool for communications and the emerging television industry. However, scientists had discovered that their oscillators could not generate frequencies beyond 300,000 MHz--a limit researchers knew they would soon need to pass. American physicist Charles Townes developed a system that used atomic vibrations in molecules to create signals within the microwave frequencies. This device, called a maser (an acronym for Microwave Amplification by the Stimulated Emission of Radiation) was essentially a microwave oscillator, just as the laser (an acronym for Light Amplification by the Stimulated Emission of Radiation) was an infrared oscillator.