The document discusses consonants in language. It begins by defining a consonant as a sound characterized by constriction or closure in the vocal tract. It notes that the number of consonants in languages is greater than letters in most alphabets, so the International Phonetic Alphabet was developed to represent each possible consonant with a unique symbol. The Latin alphabet used in English has fewer letters than consonant sounds in English, so some letters represent multiple consonants and digraphs like "sh" and "th" are used.