What characterizes a vowel sound in linguistics?

A vowel sound in linguistics is characterized by being produced without any audible friction. When pronouncing vowel sounds, the airflow from the lungs is not significantly obstructed at the vocal tract, allowing the sound to be produced smoothly and openly. This lack of constriction differentiates vowels from consonants, which often involve some level of airflow restriction that can create friction.

Vowel sounds are integral in forming syllables, as they often serve as the nucleus of syllables in many languages. This makes them essential for the rhythm and structure of speech. Their ability to be produced freely contributes to their varied representations in written language and their crucial role in phonetics and phonology.