What does “interval” refer to in music?

In music, "interval" specifically refers to the distance between two pitches, which can be measured both in terms of the number of steps between notes and the quality of those pitches, such as whether they form a major, minor, perfect, augmented, or diminished interval. This concept is fundamental in understanding melody and harmony, as intervals determine the relationships between different notes when they are played in sequence or together. Recognizing and identifying intervals is key for musicians when composing and analyzing music, as they create the building blocks of melodies and harmonies.

The other choices deal with different aspects of music theory: rhythm pertains to the timing of notes and the pattern or flow of music; harmony involves the combination of chords and how they interact; speed relates to the tempo of performance. While all these elements contribute to the overall structure and sound of a piece, it is specifically the concept of the distance between pitches that defines what an interval is in music.