Phonemes are the smallest units of sound in a language that distinguish one word from another. They are basic speech sounds perceived by speakers as a single unit, even though the actual spoken sounds can vary slightly. In English, there are about 44 phonemes, including both consonant and vowel sounds. For example, the difference between the words "cat" and "bat" lies in the initial phonemes /k/ and /b/. Phonemes are central to phonology, the study of sound systems in languages, and are represented in writing often by symbols enclosed in slashes (/ /), like /k/ for the sound at the start of "cat".