Wiktionary
n. An electronic device used to generate a signal representing the periodic value of a given mathematical function, especially sine wave, square wave, triangle wave and sawtooth wave waveforms
Wikipedia
A function generator is usually a piece of electronic test equipment or software used to generate different types of electrical waveforms over a wide range of frequencies. Some of the most common waveforms produced by the function generator are the sine, square, triangular and sawtooth shapes. These waveforms can be either repetitive or single-shot (which requires an internal or external trigger source). Integrated circuits used to generate waveforms may also be described as function generator ICs.
Although function generators cover both audio and RF frequencies, they are usually not suitable for applications that need low distortion or stable frequency signals. When those traits are required, other signal generators would be more appropriate.
Some function generators can be phase-locked to an external signal source (which may be a frequency reference) or another function generator.
Function generators are used in the development, test and repair of electronic equipment. For example, they may be used as a signal source to test amplifiers or to introduce an error signal into a control loop.
Usage examples of "function generator".
I would set up a function generator to drive the outer bubble on and off every few microseconds.
They act as an independent variable-function generator, calibrating a continuous input of data and changing operations to suit current conditions even during the processor's calculation of a problem solution.