This document discusses vowels and how they are produced in speech. It explains that vowels involve an unobstructed airflow from the lungs, and that languages vary in the number of vowels they have in their systems. It also describes how vowels are classified based on three factors: height or tongue position in the mouth, frontness or backness of tongue position, and lip rounding. Finally, it maps out the vowel space of English and labels the standard vowels according to these classification factors.