What are the characteristics used to describe vowels?

The characteristics used to describe vowels primarily include height, backness, roundness, and tension.

Height refers to the vertical positioning of the tongue during the articulation of the vowel; it can be high, mid, or low. Backness indicates how far back in the mouth the tongue is positioned, categorizing vowels as front, central, or back. Roundness describes whether the lips are rounded or unrounded during the production of the vowel sound. Tension pertains to whether the vowel is produced with a tense or lax articulation, affecting the breath control and muscle activity involved in producing the sound.

These features are crucial for distinguishing between different vowel sounds and contribute to the phonetic transcription of vowel quality within various languages. Other options contain terms that do not specifically pertain to vowel articulation or do not encapsulate the phonetic qualities that define vowels.