Like speech, the basic sounds used in singing fall into two categories - vowels and consonants. The vowels are all open sounds which flow uninterrupted from the vocal cords out through the mouth. Each vowel is given its particular sound by the shape of the mouth.
Consonants, on the other hand, are sounds which interrupt the flow of air produced by a vowel sound. Consonants are articulated by the lips, front, middle or back of the tongue, and even the throat. In general, the vowels are the long or sustained sounds in singing and the consonants are kept as short as possible.