Consonant: Phoneme pronounced with complete or partial closure of the vocal tract.

Vowel: Phoneme pronounced without any closure of the vocal tract. Usually the nucleus of a syllable.

Semivowel, semiconsonant, glide: A phoneme that is similar to a vowel but functions as syllable boundary rather than its nucleus. Used in Klingon as a possible way to analyze diphthongs as a combination of vowel and semivowel. In this case, the letters w and y, usually used as consonants, denote the semivowels [uJ] and [Ji], which are pronounced the same as the vowels [u] and [i].

Monophthong: A single vowel

Diphthong, vowel glide: Combination of two adjacent vowel sounds into one syllable, as in Klingon words like maw or yay, unless these are seen as a combination of vowel and semivowel

Fronting vs. backing: Whether the second vowel is pronounced more to the front or the back than the first (see backness). Could be used to describe Klingon diphthongs that end in y vs. those that end in w.

Monograph: A single letter that represents a single phoneme.

Multigraph: A combination of more than one letter that represents a single phoneme.

Digraph: Two letters that represent one phoneme; Klingon has ch, gh and ng.

Trigraph: Three letters that represent one phoneme; Klingon has tlh.