What do we call a letter of the alphabet that is not a vowel?

A letter of the alphabet that is not a vowel is referred to as a consonant. In the English alphabet, vowels are the letters A, E, I, O, and U, which represent specific vowel sounds. All other letters, such as B, C, D, F, and so on, are classified as consonants. These consonants can be combined with vowels to form syllables and words, contributing to the structure and pronunciation of the language. This understanding of consonants is fundamental to grasping the basics of phonetics and writing in English.