Glottal consonants

Glottal consonants, also called laryngeal consonants, are consonants articulated with the glottis. Many phoneticians consider them, or at least the so-called fricative, to be transitional states of the glottis without a point of articulation as other consonants have; in fact, some do not consider them to be consonants at all. However, glottal consonants behave as typical consonants in many languages. For example, in Arabic, most words are formed from a root C-C-C consisting of three consonants, which are inserted into templates such as or. The glottal consonants and  can occupy any of the three root consonant slots, just like "normal" consonants such as  or.

Glottal consonant in IPA
Glottal consonants in the International Phonetic Alphabet:

Characteristics
The "fricatives" are not true fricatives. This is a historical usage of the word. They instead represent transitional states of the glottis (phonation) without a specific place of articulation. is a voiceless transition. is a breathy-voiced transition, and could be transcribed as.

The glottal stop occurs in many languages. Often all vocalic onsets are preceded by a glottal stop, for example in German. The Hawaiian language writes the glottal stop as an opening single quote ‘. Some alphabets use diacritics for the glottal stop, such as hamza <ء> in the Arabic alphabet; in many languages of Mesoamerica, the Latin letter  is used for glottal stop, while in Maltese, the letter is used instead.

Because the glottis is necessarily closed for the glottal stop, it cannot be voiced.