Definition 1

“Consonant sounds are made by restricting or blocking the air flow in soe physical way, and this restriction, or release of the restriction, is what gives the consonant its characteristic sound. By contrast, vowels require the vocal tract to be open so that the air stream escapes unobstructed”.

(…)

Definition 2

“Consonants, either singly or in clusters, mark the beginnings and ends of syllables. Vowels occur as the centres or focal points of syllables, either between consonants or their own”.