This document discusses English vowels and their classification. It explains that vowels are produced with an unobstructed air stream and are approximant, voiced, and oral sounds. It then provides examples of English vowels and how they are named based on the height, position, and rounding of the tongue. Central vowels like /ə/ are distinguished from front vowels like /i/ and back vowels like /u/. Vowels can also be tense or lax. The document includes a vowel chart and discusses diphthongs like /aɪ/ and /aʊ/ which involve a glide from one vowel sound to another. It notes there is variation in vowel pronunciation across English accents.