Short answers, pulled from the story.
The word consonant comes from a Latin term meaning sounding-together, which is a linguistic calque of a Greek phrase implying these sounds cannot exist without a vowel. This ancient definition was established by the Classical Greek grammarian Dionysius Thrax and suggests that consonants are merely half-sounded elements that require a vowel to be fully pronounced.
Every spoken consonant is distinguished by a complex set of phonetic features including the manner of articulation which describes the specific obstruction and the place of articulation which identifies the exact location of the obstruction. The phonation reveals whether the vocal cords vibrate fully to create a voiced sound or remain still to produce a voiceless one, while the voice onset time indicates the precise timing of this vibration relative to the release of air.
The recently extinct Ubykh language possessed a staggering inventory of 84 consonants while maintaining only two or three vowels, and the Taa language spoken in the Kalahari Desert has been analyzed as having up to 164 consonants alongside only 30 vowels. In contrast, the Central dialect of Rotokas possesses the smallest number of consonants in the world with just six sounds and lacks even the nasals that are present in virtually all other human languages.
A blurry area exists in the classification of segments variously called semivowels, semiconsonants, or glides where the boundary between consonant and vowel dissolves. Syllabic consonants are segments articulated as consonants but occupying the nucleus of a syllable, as seen in words like church in rhotic dialects of English or in the language of Miyako in Japan where words like to build and to pull rely on consonants to function as the syllabic core.
Several languages in North America such as Mohawk lack both of the labials p and m, while the Wichita language of Oklahoma and some West African languages such as Ijo lack the consonant m on a phonemic level. A few languages on Bougainville Island and around Puget Sound such as Makah lack both of the nasals m and n altogether, and the click language Nnng lacks the sound represented by the letter m.
Linguists have devised systems such as the International Phonetic Alphabet to assign a unique and unambiguous symbol to each attested consonant since the number of speech sounds in the world's languages is much greater than the number of letters in any one alphabet. The English alphabet has fewer consonant letters than the English language has consonant sounds, so digraphs like th, sh, ch, and wh are used to extend the alphabet, though some letters and digraphs represent more than one consonant.