What is B flat?

As a music theory expert with a deep understanding of scales and keys, I can provide a comprehensive explanation of what "B flat" refers to in the context of Western music. "B flat" can refer to two different concepts: the B flat major scale and the key of B flat major.

### B Flat Major Scale
The B flat major scale is a diatonic scale that starts on the note B flat (notated as B♭). It is one of the twelve major scales in music theory, and it is constructed by following a specific pattern of whole and half steps. The pattern for a major scale is `W-W-H-W-W-W-H`, where `W` represents a whole step (two semitones) and `H` represents a half step (one semitone).

In the case of the B flat major scale, the sequence of notes is as follows:
1. B♭ (the tonic)
2. C (whole step above B♭)
3. D (whole step above C)
4. D♭ (half step above D, which is a lowered version of the natural D to maintain the major scale pattern)
5. E♭ (whole step above D♭)
6. F (whole step above E♭)
7. G (whole step above F)
8. A♭ (whole step above G)

This scale has a key signature with two flats, which are the B♭ and E♭. These are the notes that are consistently lowered by a half step throughout the key.

### Key of B Flat Major
The key of B flat major is a tonality or musical key that is based on the B flat major scale. It is one of the fifteen major and minor keys in Western music. A key is a collection of pitches, or scale degrees, that form a musical framework for a piece of music. The key of B flat major is significant because it is one of the most commonly used keys in classical music due to its technical ease for many instruments and its pleasing harmonic structure.

### Relative Minor and Parallel Minor
Every major key has a relative minor, which shares the same key signature and is based on the sixth degree of the major scale. For the key of B flat major, its relative minor is G minor. This means that the G minor scale starts on G and follows the natural minor scale pattern `W-H-W-W-H-W-W`. The G minor scale can be derived from the B flat major scale by starting on the sixth note of the B flat major scale.

Additionally, every major key also has a parallel minor, which is essentially the same scale but with a different tonic or starting note. For B flat major, its parallel minor is B flat minor. This scale is identical in terms of intervals and key signature to the B flat major scale, but it starts on B flat and is considered a minor scale due to its different tonal center and the way it is used in music.

### Significance in Music
The key of B flat major is often favored in music for several reasons:
- Technical Ease: Many instruments, including the piano, find the key of B flat major comfortable to play due to the positioning of the flats.
- Harmonic Richness: The key offers a rich harmonic palette, with the potential for complex and interesting chord progressions.
- Contrast: In orchestral and band music, the key of B flat major is often used to provide a bright and uplifting contrast to other sections in a piece.

### Conclusion
In summary, "B flat" in music theory refers to the B flat major scale and the key of B flat major. The B flat major scale is a seven-note diatonic scale that includes two flats in its key signature, B♭ and E♭. The key of B flat major is a tonality that provides a solid foundation for a wide range of musical compositions, from classical symphonies to jazz standards. Its relative minor is G minor, and its parallel minor is B flat minor, both of which are closely related to the major scale and share its key signature.

In music theory, B? major is a major scale based on B?, with pitches B?, C, D, E?, F, G, and A. Its key signature has two flats. Its relative minor is G minor and its parallel minor is B? minor.