Does anyone know what this is? I was reading a book and they mentioned this. It might be something to do with scales but I am completely unsure.
Parallel movement in intervals is when two voices (notes) move the same distance( 2nd, 3rd, 4th, ect ) in the same direction. This can be applied to any interval including 7ths. Here is an example of parallel 7ths:
As you can see, C to B is a 7th and then both move up a 2nd to D and C respectively which is another 7th creating parallel 7ths because of how the notes move. This happens again as D and C move to E and D and again once more as E and D move to F and E.
When interval motion is typically discussed it is in reference to voice leading, however typically 7ths and 2nds are left out of this discussion because the are considered to be dissonant and typically not allowed unless used in passing.