Definicja tone mark

Diacritic or non-spacing mark which represents a phonemic tone.

Tone languages are common in Southeast Asia and Africa. Since tones always accompany vowels (i.e. the syllabic nucleus) they are most frequently written using functionally independent marks attached to a vowel symbol. Some writing systems, e.g., Thai, place tone marks on consonant symbols, while Chinese doesn't mark tones at all (except when written phonemically).