Octave

In music, an octave is the interval between one musical pitch and another with half or double its frequency. The octave "relationship is a natural phenomenon which has been referred to as the 'basic miracle of music,'" the use of which is "common in most musical systems."(Cooper 1973, p.16)

Electrical relevance
In electronics design, an amplifier or filter may be stated to have a frequency response of ±6dB per octave over a particular frequency range, which signifies that the power gain changes by ±6 decibels (a factor of four in power), or more precisely 6.0206 decibels when the frequency changes by a factor of 2. This response is equivalent to ±20dB per decade (a change in frequency by a factor of 10).