A monophthong is a type of vowel sound that has a single, unchanging quality throughout its duration. Unlike diphthongs, which glide from one vowel sound to another within the same syllable, monophthongs maintain a consistent sound. Examples of monophthongs in English include the sounds in words like cat, bed, and sit. Monophthongs can be classified into two categories: short and long vowels. Short monophthongs are typically found in words like cup and pen, while long monophthongs appear in words like see and go. Understanding monophthongs is essential for studying phonetics and improving pronunciation in various languages.