The document discusses diphthongs and triphthongs. It defines diphthongs as vowel sounds in a single syllable consisting of a primary vowel sound followed by a secondary vowel sound. Triphthongs contain three consecutive vowel sounds in one syllable. The document provides examples of common diphthongs and triphthongs in English and potential pronunciation problems. It includes practice phrases to help distinguish the different diphthong and triphthong sounds.