In phonetics, what is the English "ng" sound in "sing" called?

In phonetics, the English “ng” sound in “sing” is called a voiced velar nasal.

The sound is represented by the International Phonetic Alphabet symbol ŋ. “Voiced” means the vocal folds vibrate; “velar” means the back of the tongue contacts or approaches the soft palate; and “nasal” means air escapes through the nose. You can feel the contrast by comparing ŋ in sing with the oral stop k in seek.

In English, ŋ commonly occurs at the end of words such as sing, long, and running. It also appears before velar consonants, as in sink and anger. In many accents, the spelling “ng” can represent ŋ, but spelling and pronunciation do not always match: singer often has ŋ, while finger commonly has ŋ followed by a separate g sound.

The sound is also called eng, engma, or agma. Those are alternative names, while “voiced velar nasal” is the precise descriptive term. It should not be confused with the palatal nasal /ɲ/ in Spanish ñ or the alveolar nasal /n/ in knee.