Back vowels are vowels that are pronounced using the back of the tongue.

A central vowel is a vowel that is pronounced in the central part of the tongue.

The central vowels in Japanese are 'a', 'e', 'o'.

Front vowels are pronounced using the front part of the tongue.

A front vowel is a vowel that is articulated with the front part of the tongue.

He is writing a thesis on the octovocalic theory.

A diphthong refers to the phenomenon where two vowels are pronounced consecutively within a single syllable.

Old English is a language that was spoken in England from the 5th to the 12th century.

By regularly checking the key performance indicators, you can understand the performance of the company and devise improvement measures.

Have you finished this year's big cleaning yet?