Singing is the act of producing musical sounds with the voice. Air is expelled with the diaphragm as with ordinary breathing, and the pitch is altered with the vocal cords. With the lips closed, this is called humming. A piece of music that is sung is called a song; someone who sings is called a singer.
Most singing involves shaping the voice to form words, but types of voice instrumental music which use open sounds or nonsense syllables ("vocables") also exist, for instance scat singing or yodeling. Solfege assigns certain syllables to notes in the scale.
Singing can be heard in many different places, since anyone who can speak can sing. It can be informal and just for pleasure (for example in the shower), or very formal, such as singing done professionally in a performance or in a recording studio.
Singing with no instrumental accompaniment is called a cappella. However, the Choral Journal and other vocal-related publications actively discourage the use of this term and prefer the word "unaccompanied". Nonetheless, the term is in common use in popular music for groups such as the Swingle Singers, Chapter 6 and The Bobs. Barbershop quartets are usually unaccompanied, but are rarely called a cappella.
Show choir is a combination of singing and dancing. Many schools and colleges offer show choir groups for students to participate in. Not only must participants be able to sing well and blend with a group, but they must be able to dance at the same time. This requires endurance, flexibility, and strong vocals, which can all be acquired through practice.
In hardcore punk, hoarse shouting takes the place of singing, while in emo, some bands scream rather than sing. In heavy metal, particularly the sub-genres of death metal and black metal unhumanly low growls are favored over standard singing. These styles of singing tend to make the lyrics unintelligible.
In our enlightened times, singing is by many considered to be a learnt skill. In recent years many adults who were formerly said to be unable to sing have acquired the ability while attending courses (Singing for the Tone Deaf, Can't Sing Choirs and similar).