In phonetics, a semi-vowel, also called approximant glides, is a sound that is produced by the vocal tract in a similar way to a vowel but functions as a consonant in a syllable. Semi-vowels are also known as approximants because they involve the approximation or near-closure of the articulators (e.g. lips, tongue) without creating a complete obstruction of airflow. The most common semi-vowels in English are /j/ (as in "yes" or "yellow") and /w/ (as in "kiwi").