A vowel is a type of speech sound in many languages, including English. Vowels are produced without any significant constriction or blockage of airflow in the vocal tract. In English, the primary vowels are A, E, I, O, and U. These letters can represent different sounds depending on their placement in a word and the letters surrounding them. Vowels play a crucial role in forming syllables and words. They can be short, like the A in "cat," or long, like the E in "see." Additionally, vowels can be combined to create diphthongs, which are complex sounds formed by the glide from one vowel to another, such as in the word "coin."