Electromagnetic radiation can be divided into eighty-one octaves.

an early term for octonion in algebra

a doubling or halving of frequency, in physics

An octave, in music, is the interval equivalent to an eighth. Octave may also refer to

GNU Octave, a program for performing numerical analysis, mostly compatible with MATLAB

Ottava rima, an Italian verse form

Octave (liturgical), an eight day feast in the Catholic liturgical sense

Octave (album), an album by The Moody Blues

Sicilian octave, a distinct poetic form

Octave (horse), a champion graded stakes race thoroughbred racehorse

Octave (poetry), the first eight lines of a sonnet

"The Law of Octaves" is a concept from the history of the development of the Periodic Table of Chemical Elements (see John Newlands or Mendeleev) and has nothing directly to do with music.