What are direct octaves?
So-called hidden consecutives, also called direct or covered octaves or fifths, occur when two independent parts approach a single perfect fifth or octave by similar motion instead of oblique or contrary motion. A single fifth or octave approached this way is sometimes called an exposed fifth or exposed octave.
Are direct octaves allowed?
A venerable rule of traditional Western part writing is the so-called Direct Octaves Rule (also known as Hidden or Exposed octaves), whereby similar pitch motion (i.e., two or more voices moving in the same direction) to a perfect octave should be avoided unless step motion is used.
What is hidden 5th?
: an unsounded musical interval of a fifth that is implied by the similar up or down motion of two voice parts and that if sounded would produce consecutive fifths.