There are two kinds of sounds we make while speaking - vowels and consonants. The open sounds with free breath are called vowels. The closed sounds, called consonants, are made with the breath wholly or partly checked. Consonant is a letter or sound which in speech requires hindering of the breath by the tongue, teeth, or lips.
Consonants can be stopped consonants or open consonants. Stopped consonants require complete stoppage of the breath. They are b, d, g, k, p, t. Open consonants require only partial stoppage of breath. They are l, m, n, r, w, y. The spirants are open consonants that require friction in the oral passages. They are f, j, s, v, z. H is an aspirant, or breathed, consonant.