Short answers, pulled from the story.
Singing is the art of creating music with the voice, and it is the oldest form of musical expression. Definitions vary across sources, including the act of creating musical sounds with the voice, the utterance of words or sounds in tuneful succession, and the production of musical tones by means of the human voice.
The four physical processes are respiration, phonation, resonation, and articulation. Breath is taken, sound is initiated in the larynx, the vocal resonators receive and influence the sound, and the articulators shape it into recognizable units. In practice these processes merge into one coordinated function.
Most classical music systems acknowledge seven major voice categories. Women are divided into soprano, mezzo-soprano, and contralto, while men are divided into countertenor, tenor, baritone, and bass. An eighth term, treble, applies to pre-pubescent children.
Rap does not engage with tonality the same way as singing and does not require pitch accuracy, since its words are spoken rather than sung on specific pitches. Rap historian Martin E. Connor states that rap is often defined by its very opposition to singing. Some artists use both, switching between rhythmic speech and sung pitches for contrast.
The first recorded mention of chest voice and head voice came around the 13th century, when the writers Johannes de Garlandia and Jerome of Moravia distinguished them from the throat voice. The Latin terms used were pectoris, guttoris, and capitis.
Singing has been shown to help stroke victims recover speech by training a region on the right side of the brain known as the singing center, which corresponds to the speech area in the left hemisphere. Neurologist Gottfried Schlaug describes how teaching stroke victims to sing their words can help retrain this area, since processing centers can move to other regions after trauma or brain damage.
The microphone made possible intimate, expressive styles like crooning, which would lack enough projection without amplification. It also enabled whispering sounds, humming, and mixed half-sung tones, and let hip-hop beatboxers create percussive effects with plosive p and b sounds into the mic.