What is a mode in music?

A mode in music refers to a specific type of scale that is built on a certain pattern of intervals, particularly in the context of Western music theory. The concept of modes originates from ancient Greek music and has influenced medieval music significantly.

The correct answer highlights that a mode often involves scales derived from the natural diatonic scale, which in the case mentioned, consists of only the white notes of the piano. For example, the C major scale (C D E F G A B) can serve as a source for different modes. Each mode starts on a different note of that scale, resulting in unique interval structures and tonalities, such as Ionian, Dorian, Phrygian, etc.

The other options do not accurately define a mode. A key signature indicates which notes are sharp or flat in a piece of music but does not encompass the concept of modes. A specific rhythm pattern refers to the rhythmic aspect of music rather than the tonal structure found in modes. Lastly, a style of playing strings does not pertain to scales or modes but rather to techniques used in performance. Thus, the definition provided in choice B accurately captures the essence of what a mode is in music.