Frequency is defined as:

Frequency is defined as the number of waves produced in a specific amount of time, typically measured in hertz (Hz), where one hertz equals one wave per second. This definition illustrates how frequency quantifies the rate at which waves are generated or pass a given point in a certain timeframe.

Understanding this concept is crucial in various applications, including sound and light waves, where the frequency determines pitch and color, respectively. For example, a sound wave with a higher frequency will be perceived as a higher pitch, while in the electromagnetic spectrum, different frequencies correspond to different types of radiation.

The other choices do not accurately define frequency. While the number of waves in a given distance (the first choice) relates to wavelength, it does not take time into account, which is essential for frequency. The speed of a wave (the second choice) indeed involves how fast the wave travels but is a separate quantity determined by both frequency and wavelength. Energy of a wave (the last choice) pertains to the amplitude and frequency but does not define the frequency itself.