Final answer:
A short melodic idea called a "rip" is actually known as a riff, which is a repeated chord progression or refrain that adds depth to the music.
Step-by-step explanation:
A short melodic (usually instrumental) idea called a "rip" is more accurately referred to as a riff. Option A, Riff, is the correct answer. A riff is a repeated chord progression or refrain in music, often played in the background of a song to add depth and texture. It can be melodic, but it is often characterized by a distinct rhythmic pattern. In contrast, an arpeggio (Option B) is when the notes of a chord are played in succession, either ascending or descending, rather than simultaneously. A glissando (Option C) involves sliding from one note to another, usually on a keyboard or stringed instrument. A tremolo (Option D) is a rapid repetition of a single note or alternating between two or more notes to create a trembling effect.