Consonants are sounds produced with the vocal tract restricted or completely closed. Consonants are classified in contrast to vowels, sounds produced with the vocal tract completely open. Consonants have two primary classifying characteristics: voice onset time, and location. Voice onset time refers to the amount of time that vocalized sound is emitted. Here, consonants share the customary "long" and "short" classifications with vowels. Short consonants, such as "K" or "T," are vocalized for a relatively short amount of time. We emit long consonants, such as "SH" or "M" for longer periods of time.
The place where articulation occurs is another major classifying characteristic. Articulation can occur between the lips (as in "B" or "P"), at the back of the throat (as in "K"), on the soft palette (as in "L"), or against the back of the gums (as in "N" and "T").
Different classifying systems use numerous secondary traits to further classify consonants. The International Phonetic Alphabet, for example, indexes consonants on he basis of voice onset time, location, and five other characteristics.