Learn how to say Triphthongs correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word triphthong:
a union of three vowels (letters or sounds) pronounced in one syllable (as in fire). Contrasted with diphthong, monophthong.
three written vowel characters representing the sound of a single vowel (as in beau).
mid 16th century: from French triphtongue, from tri- ‘three’, on the pattern of diphthong