A fricative is a consonant produced by forcing air through a narrow channel. The narrow channel is typically formed by bringing the tongue near the teeth or some part of the inside of the mouth. The lips and teeth can also be used to form the narrow channel through which air is forced.
By forcing air through the narrow channel it becomes turbulent. This turbulent airflow is called frication.
There are several types of fricatives. There are the sibilants /s/, /z/, /S/, /Z/,the non-sibilant fricatives /f/,
/v/, /T/ and /D/, and the pseudo-fricative /h/. Notice that the true fricatives come in voiced-unvoiced pairs.
Some of the terms we use to describe which parts of the vocal tract are used to make these fricative sounds are as follows:
labio = lips
dental = teeth
alveolar = alveolar ridge or gum line palato = hard palate or top of the mouth glottal = glottis
Labiodental means that the narrow channel is formed by the teeth and the lips.
Dental means that the teeth are making the narrow channel.
Alveolar means that the tongue is making the narrow channel with the alveolar ridge just behind the top teeth.
Palato-alveolar means that the tongue is just behind the alveolar ridge near the hard palate or top of the mouth.
Glottal means that the narrow channel is formed by the glottis. The glottis is defined as the vocal cords and the space between them.