In my understanding, Comprendida comes from "comprender" (understand). However, not sure how to understand it in the example below. Does it have a specific meaning which is not exactly related with "understanding"?
"y se llaman líneas divisorias"
Does this sentence refer to the "dos líneas verticales"? It looks the subject has been "las figuras y silencios" and it seems odd that the subject has been changed to "lineas verticales". Is this normal in Spanish?
El Compás sirve para concretar la duración de las notas y se indica con su signo respectivo al principio del trazo musical a que se refiere; las figuras y silencios correspondientes a un Compás son las comprendidas entre dos líneas verticales que atraviesan la pauta, y se llaman líneas divisorias.
The Tempo serves to realize the duration of the notes and it is indicated with it respective sign at the beginning of music chart it refers to. The music notes and silence marks to agree with a Tempo are the "comprendidas" between two vertical lines which cross through the rules, and called dividing lines.