What is a characteristic of octaves in relation to frequency?

In the context of sound and music, an octave is defined by a specific relationship between frequencies. When you move up or down an octave, the frequency is either doubled (when moving up) or halved (when moving down). For instance, if a note has a frequency of 440 Hz (the A4 note), the note one octave above it will have a frequency of 880 Hz (A5), and one octave below will be 220 Hz (A3). This consistent doubling (or halving) of frequency is a fundamental characteristic of octaves, making it the correct answer to this question.

This concept is essential not only in music theory but also in understanding sound wave behavior in general, as it relates to how we perceive pitch and musical intervals. The relationship of doubling frequency is key to forming scales and harmonies in music.