Short answers, pulled from the story.
A consonant is a speech sound produced with complete or partial closure of the vocal tract. Most consonants are pulmonic, using air from the lungs and diaphragm. They contrast with vowels, which form the nucleus of a syllable.
The Taa language has the most, reaching 87 consonants under one analysis and 164 under another. The recently extinct Ubykh language had 84 consonants alongside only 2 or 3 vowels.
The Central dialect of Rotokas has the smallest number of consonants in the world, with just six. It is spoken in Papua New Guinea.
The word consonant comes from the Latin cōnsonāns, meaning "sounding together," which was itself a calque of the Greek sýmphōnon. The Greek grammarian Dionysius Thrax coined the Greek term because he believed consonants could only be pronounced alongside vowels.
The three voiceless stops /p/, /t/, and /k/, and the two nasals /m/ and /n/ appear in nearly all of the world's languages. However, even these five are not completely universal: Arabic lacks /p/, and languages such as Makah lack both /m/ and /n/.
Voiced consonants are produced when the vocal cords vibrate fully during articulation; voiceless consonants are produced when the cords do not vibrate at all. This distinction separates pairs such as b from p, d from t, and g from k.