In the phonetic definition, a vowel is a sound, such as the English "ah" /ɑː/ or "oh" /oʊ/, produced with an open vocal tract; it is median (the air escapes along the middle of the tongue), oral (at least some of the airflow must escape through the mouth), frictionless and continuant.
Consonants are produced by pushing air up from the lungs and out through the mouth and/or nose. Airflow is disrupted by obstructions made by various combinations of vocal articulator movements, so that audible friction is produced.
